@phimarhal
I don't think I've ever mistaken a bot for a human, at least on a long enough conversation (obviously, a single short sentence can trick you). But it is going to become pretty hard, and at some point impossible, no doubt.
Pipe dream, loosely related to your project: imagine a little bot icon next to the familiar reply, recast, like under a cast. That you could top everytime you think someone is a bot. It wouldn't do anything except save those stats, so you could see your "bot accuracy". Maybe compare it with people at large too.
In my vision it wouldn't have any actual effect re: reach or anything really, just pure data game to see who do we think is real or not.