Instead of melting everything they should separate their games. Victoria 2 and Heart of Iron IV have fitting mechanics because they cover such small amount of time, but CK2 covers 684 years while EU4 covers 377 years. Because division of time periods is unlikely to happen it is always fun to to theorize what periods deserve their of game and what mechanics should they have.
769-1000 (231 years) - Dark Ages game centered around migration, viking raids and rising feudalism.
1000-1260 (260 years) - High Middle Ages game centered around the crusades, feudalism and the Mongol Invasion, almost like original CK2.
1260-1492 (232 years) - Late Medieval game centered around spread of gunpowder, decline of Mongol states.
1492-1701 (209 years) - Game that centers around rise of the west, colonization, spread of reformation and decline of feudalism, similar to EU4.
1701-1836 (135 years) - Game that centers around enlightenment, colonial independence wars and revolutionary ideals. Mix between MoTE and VIC2.