It wouldn't be able to be used for griefing (as it's easy to notify the person the "idle kick system" is in effect) and it would definitely solve the issue with idlers/afkers (which seems to be already happening in the beta, as myself and another poster reported, and could very easily happen in retail once things are for real).
Problem is that wouldn't stop the afkers one bit. All they'd need is an auto clicker, or auto mover, or any other automated scripted action to avoid the afk timer .
While I dislike thinking that kicking will be necessary at all, the way they've set up all of their core systems seems to require it. It is silly that people afking in a town get credit for quest completion. And the obviously the gamewide difficulty increase is also a problem.
Still the best/easiest and yet not perfect solution seems to be only game creator can start the vote and a necessary unanimous vote of (total players)-1 for it to kick. 4 players, need 3 to kick 1, 3 need 2 to kick 1, 2, creator can kick . Still abusable but the lesser of two evils IMO.
If kicking is implemented I'd also like some feature for the kicked/kicking players to add the opposite party to a black list though, so they don't get matched up again. That way, if you feel you were kicked by people being asshats, you just make sure you won't get matched with them again and thus have no fear of those people showcasing their asshattery again.