I like the idea of making politics and offtopic only avaiable for higher ranks. This would force shitposters to write relevant posts. There are boards like minig with very active mods who would instantly delete shitposts.

I once was participating in a forum who also provided free webspace for active posters. They obviously also had problems with users spamming the forum so they introduced a spam score (shown below the user avatar similar to the trust score in this forum.) This score showed the percentage of spam posts created by an user. And if it was above a certain value their webspace got locked. I think this would not be that hard to implement here too :0