I think a merchant republic DLC could be very, very awesome, but if it's made it should be with or after a DLC focusing on family relationships. I think the game is very well done, but the familial aspect is a bit too bland to my liking. In a Denmark game where my family (Started with Sweyn II of Denmark) had expanded a lot, where my extended dynasty (Not my vassals and most of them were independent) were Kings in Eire, Wales, England, Norway, Navarra, as well as Dukes in the Holy Lands, Southern Italy, Flanders and more - but even though this felt like an awesome achievement and it was a very good playthrough, I was a bit dismayed by the lack of options to deal with family members in other countries. If republics should be modelled, I think the familial aspect should be particularly emphasises, and the feudal system could use that as well.
That would be a wet dream for me.
But without better familial content I don't think that it'd be fun to play families living in republics. Inter-personal relations aren't good enough to model that, sadly.
