After watching a couple of streams and dev diaries I have noticed a couple of interesting things regarding the upcoming dlc's:
CK II
Building with Prestige instead of Gold: The Tribal nations will not need gold as much as the more Feudal nations do. They can use Prestige to build bu
- Managing big empires will be more difficult by limiting the number of vassals (centralization vs decentralization). Which sounds a bit weird to me because I always kept a limited number of direct vassals anyway, preferring to make use of vassal Kings..
- The Chronicle looks nice
- Added a new religion to play with; Zunist. Don't know them but I can imagine that they are implementing some unique events if they go to the trouble of adding it.
- Removed Assassinations: This was atleast the case for the Middle Francian King while playing as East Francia. I really hope that they are not going to implement this because then I can't play my assassination games anymore 
- Decadence: They will change it (again) to hopefully make it less a pain in the ass.
EU IV
- Transferring Occupation. After seizing a province, you have the opportunity to change which nation occupies it. The AI should do this as well for countries that are not strategically/historically important to them.
Marches
- Expanded Persia/Caucasus and massively expanded West-Africa and India. India got a massive overhaul, more than doubeling the amount of territories in it, as did West-Africa making both area's much more interesting to play as.
- Improved fleet management; you can now keep full maintenance for your trade fleet yet reduce it for your war fleet and you can upgrade a whole fleet at once
- Revolt risk is gone: The old Revolt Risk system has been taken apart and split into Unrest (the revolt part) and Local Autonomy (the economic part) that can be dealt with seperately
Reduced the negative penalties for Ming.