I think a good solution to district sprawling, at least early game, is to have the majority of districts needed to be built adjacent to the city center until you reach like Urbanization in the Industrial era, with Encampments, Harbors, Preserves, and possibly Industrial Zones, Holy Sites being the exception.
My suggestion, made elsewhere and earlier, was that all Districts except the specialty Settlements (including Harbors, Holy Sites, Encampments) had to be adjacent to another District, and at Start of Game, had to be adjacent to the City Center.
Later, with better Transportation/street & road building Technologies, you could be up to one District away from the city center, and along a river you could always be an extra District/tile away. This sounds very restrictive until you realize that from Start of Game you can build 7 Districts with, say, room for 35 Building Slots. Even if things like the Palace and Wonders take more than one Slot, that's still plenty of room given that Civ VI only gives you less than 30 Buildings total to construct by end of game not counting City Walls - which shouldn't go in a District anyway.
By the Modern Era, with modern personal transportation (automobiles, trucks) and paved roads, pretty much all limits except adjacency would be removed, and your cities could sprawl all over the landscape and, as IRL, absorb a lot of smaller Settlements as they go: note that Brooklyn and Bronx were separate towns from New York City before the 20th century, and once upon an Early Modern, Early Industrial time Spandau and Potsdam were separate towns/settlements from Berlin, which has now expanded to include both of them.
I kind of feel like maybe tourism should be moved over to the economy anyway. Sure, once upon a time "tourism," so to speak, may have been motivated by culture--maybe you were going on pilgrimage or you're a young gentleman going on the European tour--but what we think of tourism now is chiefly a commercial exercise. We should find something new for the culture victory.
Definitely separate modern Tourism from Cultural Influence. Let's face it, the current Tourism = Cultural Dominance makes no sense in Reality. Lots of people go to visit the Great Wall or the Pyramids of Giza, but I don't remember seeing any great wave of attempts to emulate or adopt either Egyptian or Chinese Culture as a result.
- Although, come to think of it, I could get behind a movement to lock up a bunch of current World Leaders and local politicians in massive stone structures without doors or windows, but that has nothing to do with Gaming . . .
The aspects of Cultural Domination appear to be Language, Art (styles), Music, Cinema and Literature. Use of Language is really more related to its use as a 'standard' in interCiv communication, like the predominance of French in diplomacy in the 17th - 19th centuries or the dominance of English in Scientific journals and on the Internet today - in both cases really relating to a completely Non-Cultural activity of Diplomacy and Science, and I'm not sure how that could be easily modeled in-game.
The rest are directly related to Culture in the game, and Music = Rock Bands explicitly so. Possibly, then, relate 'Cultural Dominance' to acquisition of Great People in the Arts, Music, Writing, and Great Works of those types into some kind of International Influence mechanic like Rock Bands (Art Works do 'tour' these days, but that smacks of Gaminess). Perhaps institutions, including Wonders like the Louvre or Met, that attract international attention and emulation by displaying Great Works . . .
