I think it would be neat if something could be implemented where we could marry the king/queen/empress/emperor of another country and merge our two into 1.  I could see this working well in multiplayer especially with many people playing if you 'marry' each other you form a permanent alliance together.  Could even have a little prenup type screen appear where Player Jack gets all male children and Player Gwen gets all female children and other little tidbits that could be agreed upon before entering marriage.  Just a thought