I'm assuming big expansions.
DLC: Expanded content for city states, including political game with neighbouring powers and fleets.
Update: Expanded contracts that allow a larger spectrum between proper feudalism and similar systems, allowing each state to change dynamically from or toward feudalism.
DLC: Expanded content for the steppes, including nomadic alliances mechanics, where everything from religion to marriages and military power works a bit differently. Nomads also have a different "presence" on the map.
Update: New ethinicites all over the map, and new religion mechanics that allow minority religions and cultures in each county (works great to represent the diversity within nomadic hordes, but opens new opportunities in other parts of the world as well).
DLC: Libraries and artifacts. But unlike CK2, this time it's only about the really rare stuff (so no "common swords", every ruler is able to afford that stuff...). Additionally and over the course of the game, each dynasty will build a dynastic library. It would work like the Legacy, but instead you'd build a library and fill it with books. Books can work in different ways: stat boosts, but also by replacing a specific trait when it's needed in an event. They can also open new opportunities by spending lifestyle points in reading them instead of spending them in unlocking lifestyles, like unlocking new traits or providing powerful boons. Artifacts work in a similar way - they don't just provide basic stats, they also alter the way you play with them. But people expect certain things from someone wearing a proud and fancy crown, so expect to get some stress if you don't behave like people expect your character to do. Artifacts are tied to characters and not dynasties.
Update: Some lifestyles stuff?
DLC (or stand-alone): Tales of the Summer Court - a bit like the world randomizer of CK2, but with fantasy content. The map will be filled with appropriately medieval-themed fantasy races - so no orcs and goblins, but Irish Sidhe and Fomorians, german kobolds, djinns, nordic elves and giants etc. The base game mechanics are exactly the same, but with a different skin.
Free update:?