I'd like to add my voice to the chorus of people who don't like the idea of a dungeon AFK kick feature. As others have said, it's very easy to circumvent, and it will impact innocent players as well.

I was running Cutter's Cry with some people in my FC last night when one of them started having internet problems. We waited for over 30 minutes outside the second boss's room for her to fix the problem, and most of the time we were just standing there talking in Mumble. Eventually she managed to get back on, and we finished out the instance successfully. It would have really put a sour taste in my mouth if one of us had gotten kicked from the instance because we forgot to move our character to cancel out the AFK timer while waiting for her.

Vote to kick has the potential to be abused, but it will probably solve the problem of people leeching in dungeon runs. AFK dungeon kick, on the other hand, probably won't solve much at all, and it will be an irritating feature that has the potential to ruin a run for a legitimate party. I'm afraid this will do more harm than good.