So they're just going to completely abandon their entire focus and genre just because it's easier
Yes and no.
A lot of speculation:
-Remember what Paradox people have said in their recent videos. They are no longer announcing games that are early in development, only games that are near-ish to release.
-Games that are currently "active" have their developing and designer teams working on them. As long as they are making DLCs for current iterations it is extremely unlikely that they have the next iteration of the game in development (IMO same people working on 2 different projects same time is not very efficient / smart).
-Personally i see EU living on forever. There will always be a team working either on DLC or the next game IMO. It is the flagship of the company.
-I also kinda see HoI living on forever, but to a somewhat lesser degree than EU.
-Then there is CK. The thing about CK is that it was a major hit for Paradox back when it came out. It opened up Paradox to a completely new crowd and the forum and player base exploded in numbers. Basically the current rise of Paradox is thanks to CK2. So im almost 100% sure that CK will live on, although i fully expect it to evolve heavily, specially if different project leads with new and different design ideas take it over for next iterations (a lot of people worked on CK2 over the years).
The advantages of above mentioned projects are that they already have full teams of designers working on them. People who are familiar with the setting and everything.
Problem with Victoria and Rome is that these projects (as far as i know) have been dead for ages, and their former champions, are currently working on living and extremely successful projects.
So in order to get either one of those projects to live on, you need a designer to step up and champion it, they have to assemble a whole team from scratch and delve into an extremely complicated setting. This is expensive and time consuming if you wish to create a product with complexity and quality
Thus as long as EU4, CK2 and HoI4 are alive (with big name champion-devs working on them) the chances of Rome or Victoria popping up out of nowhere are IMO very low. What is many times more likely is projects such as Stellaris, a much smaller scope game where you dont need nearly as many resources to create the world for it, and where a right game design idea (again, such as Stellaris) that fills the right niche at the right time (Cities, Stellaris etc) can be a blockbusting hit.
So my prediction for any near future new announcements is that its either a brand new IP developed by Paradox, or something developed by someone else and published by Paradox (as has been a trend in last few years).