I've seen a few threads with people complaining about leavers and suggesting some sort of punishment. I personally find it to be a problem, but also realize there are legitimate reasons for leaving games.
So this would be another way of addressing the problem of people leaving games: it should be possible to replace players that just left. This would be different from a late join; the new player would just take over the old player's situation as he left it (and it would be possible to do this after the last turn for joining has passed). This feature would be an option that could be disabled by the game host. Also, to make it easier to find these games, there could be a filter to look for games in need of replacement players.
I think this has been suggested in a post about leavers, but I couldn't find a thread.