With ageing in the game, there's a much greater emphasis on kingdoms rising and falling, succession, long-term improvement and decline of provinces, and dynastic narratives. You spend a lot longer as the lord of a kingdom and will face much more varied situations, so the strategy and kingdom management elements become very important, and require more work. Rebellions become a constant feature rather than an annoying setback in your quest for Calradia.
Without ageing in the game, none of this happens, because you're spending a lot longer in a much smaller space of time. The game becomes more about development of your particular character, doing quests and growing in power until you "win" and restart. You spend time building reputation and gold (this part of the game will have to be much more involved) until you can create your own kingdom (either after vassalage or not), and then expand until you can snowball, after which point you've won, because you're an immortal emperor who is stronger, wealthier, and more famous than anyone else in the world.
The lack of ageing also has implications for lord death/replacement, and the balance issues caused by this. Even the solution to the current snowballing problem depends on the progression of time, and the importance of ageing and death (whether it be slowing conquest much more, in fitting with a shorter progression of time, or in having vassal and cultural rebellions that reverse gains and topple empires - the vassal rebellions may be a result of a dead sovereign leaving multiple claimants).
The focus of future development is going to be different depending on how important ageing and death is to the overall experience.