How about a score/mark filter?
Basically, if you are above 10000+ score, I don't want to play you. Then that can't be abused because even if you PWN everybody, your gain will still be low because of low score.
Or if you are below 10000 score, I don't want to play you because I don't like n00bs. That's better than banning cards. Maybe if only 1 type of card could be banned per game, but even then, most decks aren't supposed to be carrying 3 types of PC, so I still think 1 is slightly broken. Score filter seems likea good idea..
Also, Mark filter is another good idea. Tired of playing Time and Entropy-bows? Then just ban them. That can prevent abuse of the system, because mark has no effect on the cards inside, I can hold deflags with pretty much any mark, banning fire mark doesn't get around it.