It really depends on what you want to do with the camera. After all, there are many great photos that have been taken with older cameras, both when they were the hot new model and when they were no longer on the cutting edge. As with all equipment recommendations it comes down to the question of what do the technical demands of the photos you want to take place upon the tools you use? If the older cameras and, more importantly, lenses can meet those demands then they are just as good for you as the newest models. If the newest models have a feature or specification that is the make or break difference between being able to create a photo or not then you need the new camera. Until you get into photography and discover exactly what it is you want to do with it it is difficult to say whether a particular model is worth the wait and additional cost over an older current model.
In terms of general photography pretty much every current DSLR and mirrorless camera on the market will do an excellent job. Most will also do video at an acceptable level as long as they have the features you require with regard to video frame rate and resolution. In the price range you are looking at most manufacturers tend to update their product about every 12-18 months, but the improvements are mostly incremental and not revolutionary. For example, the biggest difference between the canon Rebel T4i introduced in the Spring of 2012 and the succeeding T5i in early 2013 was a change in the materials used to make the rubber grip after the T4i had issues with turning white and causing an allergic reaction in a very few users.
As one moves up the price range, the product cycles lengthen considerably. Canon's current flagship camera in 2015 is the 1D X, introduced in 2012. It replaced both the APS-H 1D Mark IV (2009) and the Full Frame 1Ds Mark III (2007). Nikon's D4s was released at the beginning of 2014, replacing the 2012 D4. The only major change was a newer data processor. The preceding D3 and D3s were released in 2007 and 2009 respectively.
Unless a new model hot off the assembly line has a feature you just can't live without, usually because you need it to capture a particular kind of photograph, there's no compelling reason to wait for the next release. This is true even if a particular model appears to be at the end of its product life cycle unless you are more concerned with how much you might be able to resell it for than you are about using it to take pictures.
Here's a specific example from my own personal experience:
The Canon EOS 7D was introduced in the Fall of 2009. I decided in early 2012 to upgrade my heavily used 50D (introduced late 2008) to the 7D. The two models were introduced less than a year apart but were sold concurrently until the 60D succeeded the 50D in late 2010. The 7D was a step up from the mid-range enthusiast model 50D to an advanced prosumer camera that offered a more sophisticated and configurable focus system as well as faster burst performance. Both features were important to the action and sports I shoot frequently.
By the time I bought my 7D in 2012, there were already persistent rumors of the impending release of the replacement for the 7D. These continued to swirl for the next three years! I pretty much ignored them. I didn't plan on buying another APS-C again. Ever.
At the time I got my 7D, I was also using a full frame 5D Mark II. It was, and still is, a great camera but just a little too slow for sports in terms of focus speed and burst rate. The 5D Mark III that replaced it, however, had a top of the line AF system and a fast enough frame rate that it just could do what I needed for night sports. And the image quality difference between the APS-C 7D and the FF 5D Mark III is significant, especially when shooting in low light. So once I bought a 5DIII I started using it more for night sports and continued to use the 7D when shooting sports or other action in better light. I used the 5DIII for pretty much everything else I shot.
Then in late 2014 the 7D Mark II was released. I still had no plans to purchase one until I read about a new feature introduced that might directly impact what I shoot the most: night sports under flickering stadium lights. I took a wait and see approach and read several hands on reviews from sources I trust to be sure the new feature actually works as advertised. Satisfied that it could make a difference in the specific work that I do, I got a 7D Mark II in August 2015 just before the beginning of the fall football season.
With the "anti-flicker" feature enabled, my keeper rate has gone up significantly. Every frame is exposed when the lights are peaking! Every frame has the same exposure and color! No more frames that are dark brown from being exposed when the lights were in the dimmest part of their cycle. No more frames well exposed on one side and brown on the other as the lights were on the up or down swing as the slit in the shutter curtain transits across the sensor! And because the shutter always opens when the lights are peaking, I can get about 1/2 to 2/3 stops faster shutter speed at the same ISO and aperture!
For me and the type of photos I take, the 7DII was just the thing I needed that no previous camera has ever offered. For someone not needing fast shutter speeds under flickering 120Hz lights (and restricted from using flash), it might be only incrementally better if even better at all than what they already have.