It is certainly theoretically possible, at least with the mechanical designs of some older lens mounts, particularly with the relatively large amount of space afforded by adapting lenses with 40+ millimeter registration distances to cameras with 20mm or less registration distances.
The most likely reason we haven't seen any¹ is that there is no real market demand for such a device. I can think of several factors that might be in play:
- Using older manual focus lens mounts means the user is already giving up autofocus. This usually also means they're using such lenses is a way that allows plenty of time to set up a shot. (No one is using adapted manual focus lenses to shoot sports action for hire.)
- Most of those shooters comfortable with focusing manually are also comfortable setting exposure manually. They're happy to use either an external light meter, or to dial in exposure by taking test shots and using the histogram to adjust for the next shot.
- One of the main motivations for using older lenses on newer cameras is to lower costs as much as possible. Lenses in older, pre-AF mounts tend to be cheap and plentiful. Simple mechanical adapters are cheaper than would be the case for complex mechanical adapters that would measure a mechanical position of a pin/lever and translate that to an electrical communication to the camera body.
¹ For all I know, such a thing may actually exist somewhere. But if they do, they're not widespread or well known.