I don't think this is too far from the truth. IIRC they want DLCs to not break the game for multiplayer - read - they want people who have a certain DLC to be able to play against someone who doesn't. That means it changes purely aesthetic things like Skin, Clothing, Sprites, Music. Since we've already gotten Music here is my guesses:
- A big expansion for Character appearances (skin, hair, shapes)
- A big clothing expansion (head gear, shirts, different cultures)
- A sprite expansion (regional stuff, religious stuff, maybe tiered changes)
- A religious expansion (new icons for the different religions as well as special clothes for priests/imams)
That is what I think. Honestly, I am okay with that. I'll probably grab one or two, but not all of them. Never got any of the EU3 sprite packs, but I know for some people it is an important thing.