CK3 might be a bit latter than that, if you assume that Stellaris and HOI4 get CK2 length development cycles and Vicky 3 is in the interim.
Except Paradox has grown as a studio a lot more than one game needs, they could proably even speed development up, but I doubt they'd do that because they'd start competing with themselves.
Even best case scenario Vicky 3 isn't going to sell that many copies (compared to CK/EU/Stellaris) so I highly doubt a large team would or budget be allocated towards that venture. Besides that Paradox has grown exponentially the past 4-5 years and is financially capable of developing multiple games at once. Now that HOI4 and Stellaris are released I'm sure more than one big project is in the works all things considered.
You don't think? Vic2 has by far the most loyal fanbase, and is generally still considered their best game by anyone who's learned to play it. I have no doubt that they are longing to get back to Vic with all the resources they have in their new post ck2 incarnation.
I think dropping EU is more likely than dropping vic because eu is the series that is the weakest, it's so bound by it's own legacy as a boardgame simulator. So yes I think vic3 is likelier than eu5 is. And ck3 more likely than both.
I'm confused as to why people believe naval battles are impossible. The game is on the same engine as EU4. I do admit I'm ignorant on the technical stuff, and am aware implementing naval battles would require massive rewrites, but I'm positive it's in the realm of possibility. (And really should've been implemented by now)
Naval battles are important, just because paradox has never gotten it right yet (though hoi4 seems to be handling it somewhat well in a more minimalist way) doesn't mean it's not something that should be represented well in their games.
I may be partial because my first job was as a tour guide at the national maritime museum of sweden, but seas and rivers are key to so many things. And also a factor that a lot of people overlook meaning they really have a chance to actually teach some history here.