-Allowing tiles to switch owner because of culture (maybe cities as well)
Certainly not. The reason why it was removed was that conquering old enemy cities was making them useless since you could not exploit the land around, invaded that it was by this same enemy culture. To profit from it, you had to take every of surrounding cities and even raze them, because if you simply took them the problem was repeting exponentially. This was a heck of a major frustration and added to war weariness something really funny sometimes. Without war weariness it would be less a pain but it's far better as it is in Civ5. I didn't know city flipping was back with Brave New World, it could be interesting or at least give something really usefull to simulate with culture, which is more an annoyance than anything else actually. Definitely territory acquisition should be totally rethought, I don't mind Civ2 one where the first working a tile own it (on frontiers with another civ) and a fix big fat cross, except that indeed that those big fat cross could be crossed by any enemy military unit without a ROP, for surprise attacks included what sounds very funny nowadays. The fact is that big fat crosses were lightly recognized as our non violable territory by those days. In fact, culture limits don't add anything to how big fat cross should have been managed, we could perfectly make them non violable except with a ROP, not only to say that the problem of seeing enemy units in odd non big fat crosses of our own places is actually the very same in Civ5. Not only culture doesn't change that, but it doesn't answer no more to how tiles should be acquired.
As I said multiple times already in those very forums, territory acquisition makes senses in a game named Civilization, but actually what we rule are more nations in their concept as the name of the different civilization let us know (France, USA, Germany, England, Spain, Italy etc... instead of Occidental Civilization for example) : except from culture, we are controlling wars, treasury, science (even if its concern as a nation concern is overly disproportionnaly emphasised, which make it more a 'civ' concept, but science do not depend on gold nor population, but it's the developers job to find something convincing - good luck if you don't want to go away from the accessible and mainstream 'pushing unit' concept !), territory for the most part (planting cities, heh true) etc...
A real civilization should acquire territory organically and have overlapping territories influencing each others. Wars should be designed within this system, as long as we consider them as a manifestation of culture. You shouldn't be able to control every aspect of citizens life as a King player, but play with a range of factors influencing your world a la Sim Earth as a God player. Granted, it would be a totally different game, you could even make it real time instead of turn based a la Sim City, but for a time it would changing and a real evolution of the series that has known very basic AND maintream beginnings. (not to mention followings, endings included) I think keeping the series as basic is an error, as a player we shouldn't be able to control it totally as to know exactly what formula does what like in Pokemon For Hardcore Gamers games (silly you, silly ; stuffy, mind influencing, heady, stultifying and insulating, peace to your souls "gamers"), but only influence it with an idea of causes and consequences that should be kept as realistic as possible to be playable without reading a 400 page handbook. Still to have more than a mere degree in History that only count facts without trying to explain them. That's it, Civilization developers should convert into a new type of scientists ! :crazy: