I think Europe's theatre needs more attention from the developers than the rest of the world. The last DLC have all been about the Americas and Far East Asia. Actually, I know what I want. I want an overhaul of the naval battle system where the nation that has the most ships in a stack will always win a battle. See how that worked in the Franco-Dutch War of the second half of the 17th Century. The Franco-English fleet was overwhelming the Dutch one, still De Ruyter was able to thwart that threat with skillful maneuvering and a defensive stance. Naval battles should be a seasonal thing as they were in those times and they shouldn't result in total destruction. Ship capturing and destruction was not the norm in those days (if you consider the number of ships implicated in a battle versus what was left after a battle).
The problem with making ship battles not-total destruction is that then there's no decisive winners. Loser goes home, repairs at port, then comes right back out a year later and laughs in your face again.