Don't forget alien invasions!
Seriously though, I agree that it will start with the sprites and music packs like always. However, I would like to see something akin to the Create-a-Ruler like they have in CK2 but based on your kingdom. Go for some mind boggling crazy mixtures, or, create that nation YOU always wanted to play. Something like that would be cool.
This, I would pay for this type of feature in a heartbeat. No question in my mind this type of DLC has to be released at some point, especially after releasing the Create a Ruler DLC in CK2