I think the problem is too many peope are worried about their ratings. If you get a bad opponent, just quit yourself. Stop worrying about your ratings. They don't mean anything, they are just a guide as to your approximate strength. I was playing a game with this idiot who after 3 moves into the game starting making racist remarks about Obama. Since I refuse to play any racist, I just said "You know what? Goodbye" & quit my game. I lost 30 rating points. But you know what? Big deal. So I have an extra loss to my record. The loss & ratings drop isn't going to make me any better or worse as a player. So my opinion is if you're playing someone who annoys, offends, or is a racist, just quit your game.
You'l actually feel a lot better
Interesting discussion.
One thing the site could do is to track such a metric behind the scenes, and then to see if it matches up against abuse reports.
Also one point you haven't addressed is how increments would play a role. If I'm playing a 30 30 game (which I would never do LOL) but if I were, then it's not nearly as big a deal for me to flag when my previous move was made with 1 min left.
This is the only option I find reasonable.