A pop system of some kind is by far the best way of implementing things like a more nuanced culture and religious system, as well as a better development system. If you don't model the population of the regions in some manner, you're inevitably stuck with the sort or kludgy implementations that EU4 has, because you're trying to model a reasonably realistic system without the thing that actually drives those things in real life.
Best way? Debatable, but not really my point. Given the amount of bugs people complain about, I'm not one of them, my point is that adding some complicated pop system doesn't reduce the bugs in the game it increases them.
Since we're on the topic of a pop system. Realistic? Yeah, a game that lets me conquer the world by 1821 isn't going for realism. So that argument doesn't appeal to me. Does it improve game play? Considering the many other games that have pops it isn't likely. It'll end up being another micromanagement system that doesn't add anything to what is currently being used in the game and pretty much every other iteration of EU since the first title. Putting jobs and managing populations where they work like Stellaris, or implementing a Victoria style system where you had production of many resources so you can change their strata seems even less fun. It works for those games because Stellaris doesn't have much else to micromanage, and in Victoria the shorter time span made it less of a chore. This of course ignores how awful the AI is currently bad at managing the many different mechanics in EUIV adding another one it will mismanage is just adding more fuel to endless posts complaining that AI doesn't do X correctly. Other games that have pop system tend to be turn base and thus those choices have more impact since typically those games have winning conditions and the options of what else they could be doing are more impactful at the time. I.E. Civ IV and later having a pop produce more hammers, culture, science, or money in a game that lasts a certain number of turns are real choices.
Lastly, given how the devs have implemented mechanics in EU series, it will either be the previously mentioned micromanagement, or yet another system in which players can achieve maximum efficiency (where the AI won't) causing more power creep, that allows for even more blobbing. I doubt highly it will give me as a player real strategic choices.
Edit: Adding to the last bit, I'm a strategy gamer, and while I wish EU was more than a map painter it isn't. No matter the limitations I put on myself, all goals revolve around either conquering an area and or colonizing. I enjoy the strategic challenges that it offers from a historical perspective but realizing that realism isn't a factor here. It is fun playing Ireland, an HRE minor, the Aztecs, Korea, etc... but I really don't see how adding a pop system enhances those things, aside from either being annoying or making it easy. In either case it would be less fun.
