Since this is about EU4 and likely a new engine, maybe it should feature a mix of turn-based and realtime. Suppose we are talking SP only for a minute. Now imagine, you are at peace, and basically all you do is pause the game once or twice a year to use your specialists. How about you could set the game to run in turns of the length of your pausing interval (and set that interval mid-session)? Once you hit ´end turn´ the game will, behind the scenes, run normally, but it wont display anything, except the date it is working on right now. Everything progresses just as in realtime during the ´AIs turn´. Events might still pop up during it. Certain events throw you back into realtime (being declared war upon, is obviously one of these).
I´d probably use such a feature quite often, not only in EU4, but also in, say, HoI4, where i´d probably have two meetings (=turns) a day during war-time and maybe one per month in peace.
The value such a feature would add to the franchises would go beyond mere functionality, as the flow of time within a game greatly contributes to the consistency of its atmosphere, for me. I assume, some people simply put the speed to max and have the game pause on everything and then decide whenever something comes up. But, for me, when, say, 20 years pass in the game, it just feels odd (like some sort of amnesia) when they fly by in 30 seconds - i either want to wait for some time (!), or hit ´end turn´ a number of times i find appropriate. --- I dunno - i am probably not explaining it convincingly.
Besides that, i dont want to switch to another game each time i feel like doing TBS rather than RTSish.