I'm also in the "it's far too soon for CK2 to be getting a sequel". While die-hard fans of a franchise will always want more (I want a new HoI every year, and I want it now! OK, not really

), it makes a lot more sense for Paradox to continue to develop a broad base of games, rather than double down on CK. In this context, I'd very much want to see Rome and Victoria continue as 'active' franchises, rather than be put out to pasture (and that's just talking from a business development perspective - for me as a player, I'd be rather sad indeed if it happened!)
On CK2, I've 'only' played around 350 hours of it, because until conclave it had never 'clicked' with me as much as EU, Vicky or HoI (Conclave's turned that around a bit, I'm enjoying it a lot more now), but it's clear that the game has a ton of depth. If they stopped developing it tomorrow (which I hope they don't, of course), then I reckon there at least a couple of thousand of gameplay hours of fun to be had with no further development and not using mods (as is the case for all PDS games, really). Given that, I think rapid-fire sequels are a bit of a waste (even for HoI and Vicky

) - space 'em out, give the mid-level fans enough time for their appetite to build again, then strike!
Another thing to keep in mind is that a longer gap means greater potential for game design to be supported by limited technological progress.