I don't see why they couldn't allow a simple 5-10 'game block' list where you can add people that you truly never to want to play again. If you limit it to only 5-10 it can't be abused.
Although I rarely seem to run into the same 'trolls' twice, at least as far as I can remember. The really really bad ones stand out and they're pretty rare like 1 in 50 games where I'd actually want to permanently block them from ever being in my games again. Only if they're actually intentionally messing up the game (ping spam abuse, constant intentional feeding, berating team members all game, etc). Sure I get a lot of minor trolls inbetween but the big game ruiners are rare.
I actually think it would reduce a lot of hate/resentment after games, and would make players think about the situation more rationally. When they're considering adding someone to their 'game block list' they'd compare them to the others they've blocked before, and think maybe this guy wasn't as bad compared to the others so I won't block him, and if he was worse then you can go ahead and game block him. It's a small condolence for having your game ruined, but at least you can know he won't be in your games again. (Smurfs, i know, but at least one account is blocked)