I'm sure paradox would love to rope in Kaiserreich and make money off of it. But kaiserreichs development team, if it can even be called, is really more of a massive group of random people who have contributed bits and pieces over years. You know that long series of pop ups at the beginning of every new game? Not there for giggles.
Then it runs into questions like: Who owns the rights to it? How would they determine who gets what percentage? What is that massive amount of effort worth to the Kaiserreich team? What is that effect worth to paradox? Would it even be worth paradox shelling out for what was already free publicity and sales driving in the first place? What kind of precedent would that set for other mods?
There's a lot more to it than "Paradox buys Kaiserreich" and im sure paradox's legal team scream bloody murder and torpedo that idea as soon as it left someone's mouth.
It'll come down to two things: Will HoI4 be flexible enough for KR? And will the KR team be willing to put forth the effort to port it? From what paradox has been saying in the DD responses, it should be flexible. So it all hinges on the second question.