A new Hearts of Iron can possibly be even more complex then the current one. (If they go the same route as happend when they went from HoI2 -> HoI3).
If that is the case then the AI will have an even harder time to keep up.
In short, an engine like you want "without limitations" would spell disaster for the AI, the reason the AI appeared to be more competent in HoI2 was because the game was so much more simple, there wasn't so many things you could do wrong...
All i would have liked to see is an engine that opens more doors for modders. But if not possible at the moment then no need to think about it. (Well, untill HOI 4 that is.)
If you don't think the current engine is moddable you need to try to mod some other strategy games, seriously!
I also think most players use counters so they don't care about unit textures really
Dude i love HOI 3. Almost 200 hours played and still loving it, also have tried many mods, hence why i would have liked to see more, did not just know earlier that the engine was limiting them. (Or the game developers that matter since some things cant be implemented.)
Also did you mean like Supreme Commander, C&C. World In Conflict, Wargame European Escalation, Total War series? And i could go on.
I do play strategy games, a lot of them, love them. ^_^
And yes i use the counters too. And i did not mean unit textures. Embarrasingly enough i meant the unit picture on production tab. (They are crap, and kind of bug me everytime when making a unit since if im going to seeing something a lot it could be atleast good looking.) Same could be said about the unit textures perhaps but i prefer the counters.