Normally it's not that big a deal to buy a recently discontinued interchangeable lens camera body. As this answer and this answer to the question [A digital camera I'm interested in is being discontinued. Is it ok if I still buy it? ] make clear, when a camera maker introduces a new replacement for a camera they continue to support that camera for an extended time period. Canon, for instance, supports repairs of their discontinued lenses and bodies for at least seven years after they are discontinued. Most camera makers also continue to produce newer improved products for the system to which the discontinued camera belongs. Lenses, flashes, etc. made in the same system will almost always work with older cameras made in that system.
With the Nikon 1 series it's a bit different. This is because the Nikon 1 series, of which the J5 was the last model offered, is the only system that uses the Nikon CX mount. Not only is the J5 being discontinued, it appears the entire Nikon 1/CX system is going defunct. One would expect Nikon to continue to provide repair and other support as required by the various laws of different countries in which they sell cameras. But beyond that, it's unclear how long one could expect Nikon to support a Nikon 1 series camera, lens. or other accessory.
What is clear is that no new CX lenses or other accessories can be expected in the future as well as no new Nikon 1 series cameras.
As to the rest of it, a little historical perspective might give some clues as to how Nikon may be changing some of their basic philosophy regarding compatibility between older and newer products.
Back when the semiconductor revolution arrived in force in the camera industry in the 1980s all of the then-current players selling cameras had a choice to make: try to update their current systems to offer the enhanced capability that electronic processing and control systems offered or scrap their current mechanical systems and start fresh with a new system built around the enhanced capabilities of integrated circuits and electronic communication between various parts of an imaging system. Many camera makers had previously adopted electronic shutters or electronic auto exposure systems. But all of those were part of the camera only. Prior to the mid-1980s no mainstream 35mm camera had any electronic connection to interchangeable lenses.
Of the major players at the time, Nikon and Pentax chose the first option. Canon and Minolta - now part of Sony - chose the later. Especially in the case of Canon, the decision was not without controversy. Minolta was more of a consumer brand where buyers tend to buy a camera and most of their lenses at the initial purchase, so it wasn't near as big a deal when Minolta introduced a totally new mount and system in 1985. Depending on what region of the world you were in, Minolta marketed their new system as Maxxum (North America), α (Asia), or AF which was later renamed Dynax (Europe).
Many pros shooting with the Canon FD mount system felt abandoned and betrayed. Their substantial investment in FD lenses and bodies took a tremendous hit. Sure, they could continue to shoot the latest films in their FD cameras. But they could not expect any new lenses or other improvements, including the entire autofocus revolution beginning to take place, to the FD system. Anyone shooting the Canon FD system more or less realized they were eventually going to have to "start over" building a new kit with another system at the same time as the value of their current Canon FD lenses and bodies plummeted.
Nikon, and to a lesser degree Pentax (who kept the same mount but almost immediately started adding additional mechanical and electronic connections that added additional functionality), chose to keep most all of the new electronics in the camera body and continue their current system of mechanical connections between the body and lens. This meant older Nikon and Pentax lenses could be used on the newer electronic bodies, they just would not have the full capability of the newer lenses. Those invested in the Nikon and Pentax systems didn't need to reboot and start over with another system. They could gradually update different parts of their kit as needed.
In the short term it seemed like Nikon made the best choice. Many Canon FD shooters, particularly those pros who had been using Canon, switched to Nikon. Nikon already had the largest share of the pro market. While many who swapped did so out of resentment for Canon's decision to more or less abandon the FD system (Canon still provided service and repair for several years, but introduced only a few new products in the FD mount for a very short period after the introduction of the EOS system), others did so out of pure necessity. It took a few years for Canon to introduce a full range of bodies and lenses in the new EOS system. In the interim pros had to either stay with the frozen-in-time FD mount, use dual systems (The new EOS mount for what was available and the older FD mount for what wasn't), or go to a different camera maker that offered a full range of lenses.
By electing to go with a clean slate Canon designed an entire system around an all-electronic connection between camera and lens. They also took the opportunity to increase the throat diameter of the new mount so as to allow wider apertures at wider angles of view. Apertures could be controlled faster and more precisely with no need for periodic calibration and adjustment of mechanical linkages between camera and lens. Autofocus motors could be optimized for a particular lens and the specific focus elements that each motor for each lens needed to move. They could be placed inside the lens without a need for mechanical connections between the body and lens and the need for different gearing, which also meant slower focusing, for the heavier focusing elements of large telephoto lenses.
As technology moved on, the capabilities of an all-electronic system began to prove themselves. Nowhere was this more obvious than in the difference between all-electronically controlled AF systems and mechanically linked AF systems. With the introduction, between 1987 and 1991, of a full range of fast telephoto lenses with the UltraSonic Motor and the resulting quantum leap in AF speed and performance over previous AF systems, Canon began to dominate the pro sports/action market almost overnight. Then came the development of IS (lens based optical image stabilization).
For most of the period since Minolta (1985) and Canon (1987) introduced camera systems with an all electronic mount, Nikon has gradually introduced electronic connections to the F-mount system in several piecemeal stages.
Nikon had introduced their first autofocus F-mount lenses (designated AF) in 1986. The lens had no autofocus motor. The focusing elements in the lens were geared to a shaft driven by a motor inside autofocus capable bodies via a "screw drive" mechanical connection. Even older "pre-AI" Nikon F-mount bodies made prior to 1977 could use these lenses as manually focused ones by installing a new aperture ring with a "pre-AI" type coupling prong. Nikon offered factory conversion of such lenses.
Nikon introduced 'D-type' lenses in 1992 that electronically communicate the focus distance to the camera. Earlier F-mount cameras could still use 'D' lenses, they just didn't include the enhanced capability of distance reporting. Even pre-1977 F-mount bodies could use 'D' lenses if an aperture ring with a prong was added to the lens.
Later in 1992 they introduced AF motors inside the lens (designated AF-I) that required electrical connections to power and control the in-lens AF motor. The only AF-I lenses were longer focal length telephoto lenses. Such lenses have heavier focusing elements and prior to the AF-I lenses this would have required reduction gearing that limited how fast an AF motor in the camera body could focus the lens. (At this point in time Canon already had a fairly full range of fast telephoto USM lenses in place while Nikon had no AF lenses longer than 300mm.) Older F-mount bodies not capable of controlling autofocus of AF-I lenses could still use AF-I lenses by manually focusing them. Again, even pre-1977 bodies could use them with manual focus by adding a pronged aperture ring. And Nikon continued to build all of their camera bodies with the capability to be able to accommodate either an AF-I lens with a motor in the lens or an AF lens driven via a mechanical screw drive connection to the AF motor in the camera body. (Only in the 2000s with the introduction of consumer level DSLRs did Nikon start making F-mount bodies with no 'screw drive' AF motor in F-mount cameras that were capable of autofocus with AF-S lenses.)
Nikon didn't introduce the first lenses (designated AF-S) with SWM ('silent wave motor' - analogous to Canon's USM) AF motors until 1998, 11 years after Canon introduced the first USM lens. By then Canon had completely dominated the pro sports/action market for over half a decade. All AF-S lenses (prior to the 'G series' introduced in 2003 - see below) could still be used with all Nikon F-mount bodies if a prong was added for use with pre-1977 bodies.
Throughout all of these modifications and additions, Nikon stubbornly clung to exclusively using a mechanical aperture connection for almost two more decades following the landmark changes that began in the late 1980s. It was the lynchpin upon which the entire concept of backwards compatibility of newer cameras and lenses with previous F-mount lenses and cameras hung.
Lately, though, even the F-mount has seen changes that don't allow newer lenses to work on (not that much) older F-mount bodies. Likewise, beginning with the introduction of consumer grade digital bodies, the idea of newer bodies being able to use (not that much) older lens designs was also abandoned.
In 2003 Nikon introduced the 'G series' lenses with no aperture ring on the lens. The aperture must be set using the camera body. This requires electronic communication between the camera and lens. Older Nikon F-mount bodies without the electronic communication capability (i.e. any manual focus F-mount Nikon body) can not control the aperture of 'G' lenses. Even though the camera and 'G' lens communicate electronically and even though older Nikon bodies were useless with them, the aperture was still actuated via the clunky old mechanical connection Nikon has used since the late 1950s!
The introduction of 'G' lenses was the first time Nikon had allowed a major new class of lenses to leave behind the idea that all F-mount lenses¹ were functional, to one degree or another, on all Nikon F-mount bodies.
¹ There were a few isolated exceptions, such as the earliest F-mount fisheye lenses that protruded deep into the mirror box and required full-time mirror lockup. When such lenses were used there was no internal metering nor any way to use the optical viewfinder because the mirror could not be let down with the lens attached.
In 2008 Nikon introduced electronic aperture diaphragm control ('E type' - not to be confused with earlier 'E series' lenses that were budget AI-S lenses) for the first time, but only with several PC-E (tilt/shift) lenses. They don't work with any F-mount bodies introduced before 2007. Later, around 2015 or so, Nikon began making other lenses with 'E' aperture control. Most of the 'E' lenses introduced by Nikon are fairly expensive high end models. NO 'E type' lenses can have their aperture controlled by any F-mount body introduced before 2007. Unless they are also an AF-P lens (see below) , 'E' lenses can be used with the aperture wide open and focused manually with older F-mount bodies.
In 2016 Nikon began releasing AF-P lenses, which have a stepper motor similar to the STM AF motor introduced by Canon back in 2012. AF-P lenses don't AF with Nikon cameras made before 2013 (In contrast, every Canon STM lens fully works - they can be used with both autofocus or manual focus - with every EOS body Canon has ever made since 1987 when the EOS system was introduced). Since AF-P is focus-by-wire only, they can't even be manually focused by non-compatible camera bodies, not even the older highest end bodies such as the $6,000 D4 (2012) or $3,000 D800 (2012).
So, what can we learn from history?
First, a couple of observations about the Nikon 1 system.
- It was the first Nikon interchangeable lens system with an all electronic connection between the camera and lens. It only took Nikon well over 20 years longer than Minolta and Canon.
- Unlike the F-mount system, which was well-established and entrenched among professional photographers by the 1980s, the Nikon 1 system was pretty much a consumer system.
- Nikon is struggling with the disappearance of the entire casual camera user market (there is no market for cameras to take snapshots, unless you are selling a smartphone) and looking to eliminate as much red ink as it can.
Without the weight of a well established system of cameras, lenses, and most importantly, a base of users that can be expected to constantly upgrade the system they are shooting I don't expect to see very much concern from Nikon to do anything beyond what they are legally required to support with regard to warranty coverage of the products in the Nikon 1/CX mount system.