I once challenged my friends to run a deck that had the title: all cultures must help! You had to make a deck that had at least Rohan, Gondor, Gandalf, Elven, Dwarven and Hobbits and each culture had to have the same ammount of cards. Optional you could add Smeagol, but the same rules applied. So with all 7 freeps cultures and you wanted not to grow too big you where looking at a 35 sized deck, so each culture could bring 5 cards.
Oh and on the flip side, you couldn't have cards that took advantage of mulitculture decks like
Grima CC. I love these challenges, and I love multiculti. The more cultures involved, the happier I will be!