I've come up with a lot of Nomic-type ideas that might have potential, but might not work out in reality. CivNomic was the discussion a while ago (Civilization with Nomic-style rule changing), but the biggest problem would be coming up with a way for it to work without it suffering from the problems that Nomopoly IV did (strong players getting stronger, players with a bad start having no chance, etc.)
Nomopoly seems to be the easiest game to make work, since there's really no initial direction for the game to go. If anyone has any other ideas, feel free to let me know, and maybe the next game could be something different!