Improve the game mechanics for the actual period. And make a great Vicky 3. Why would you want 1 mediocre game that struggles to represent a long time frame when you can have 2 great games that fit well into their respective time periods?
And about the comparison between EU4 and CK2, these are so different games that you could very well compare Civilization 6 and EU4. They have NOTHING in common, just that Paradox is behind both CK2 and EU4. It's the only thing they have in common. They could very well make a new game that covers EU4 period but focusing in you character and your family (CK2) and also the other way: Make a game that covers CK2 time frame but based in countries and empires, not in dynasties. Every game would appeal different players, even when I am sure 75% of the players play both eu4 and ck2 and enjoy both in different ways.
And about the comparison between EU4 and CK2, these are so different games that you could very well compare Civilization 6 and EU4. They have NOTHING in common, just that Paradox is behind both CK2 and EU4. It's the only thing they have in common. They could very well make a new game that covers EU4 period but focusing in you character and your family (CK2) and also the other way: Make a game that covers CK2 time frame but based in countries and empires, not in dynasties. Every game would appeal different players, even when I am sure 75% of the players play both eu4 and ck2 and enjoy both in different ways.