A rep system on Isotropic would be very hard to get right.
A lot of people take losses personally and there's a lot of room for miscommunication in text-based chat with strangers. I've had people take "gg" the wrong way, for instance. Would people down-vote to get back at you for feeding them 10 curses or opting for a winning Scrying Pool engine? Almost certainly. Further, it's annoying enough trying to auto-match without having one more reason to reject games. Also, those who get very negative reputations can very easily create a new account with a clean slate while serious players would not do this, so you punish the wrong people.
My preference: give me an auto-match blacklist. Let me blacklist someone for either 5 minutes or (semi-)permanently, and let me manage the list, in case I misclick or have a change of heart. Potentially investigate, suspend, or otherwise punish people who have a high number of permanent blacklists. 5 minutes would cover the case where auto-match keeps suggesting a game with someone I don't want to play with (maybe someone who is cherry-picking games).