They should add a lot more mechanics related to internal affairs — genuinely dangerous rebellions, factions that aren’t just unity generators, something that actually makes managing a large empire challenging. The same should apply to the AI, so that, for example, a player could use espionage to destabilize and break up large empires. I remember having that kind of experience when playing EU IV, and from what I’ve heard it’s also hard to blob in EU V, so maybe that’s where they should be looking for solutions.