A lot would, to be sure, but I'm not sure it would be good. I mean, the games are all about balance. And when the player finishes a game, usually he's the first world power. And HoI4 is already very easy (and to be honest it's not good, Darkest Hour was far better), so for instance an industrialized China which would've conquered all of Asia in HoI4 would be OP and destroy everyone without any difficulty. For the CK2 -> EU4 conversion, a lot of people, to still have challenge, chose to play another country to fight against the one they were playing in the previous game.
And HoI4 is too much around tree focuses for the conversion to be effective.