that sounds good in theory, but this idea sounds alot like playing risk at another site where you open the games players join and you can surrender and leave anytime, players dont just leave if they cant win, they leave if they are not in good position.
If you want to play or join a game you should be committed to it 100% whether you are about to win or not. Even if your just there for the amusement of whoever IS winning.
The resign button issue would open door to hundreds of players just leaving after the first few rounds. Games wouldnt last much longer, best case scenario it would be down to 2 people for a few rounds and then a winner.
As it stands you are FORCED to stay in any game you join, so you might as well make something out of it. Thats how it should be, no change needed.