Keep as separate districts: encampments, aerodromes, harbors, the green districts(aqueducts, dams etc.), wonders. Put everything else back in the city center. While deepening city planning to a degree is good, I think 6 went too far by district-ifying 90% of buildings. I think it made city building too micromanagey - Civ is a 4X game, not a city sim game. Having things like harbors and encampments and dams separate from the city center makes sense and even has practical benefits, but I don't see any particular reason campuses and commercial hubs should be that way, and it also means sometimes you have to give up a resource because it's on a tile with a good adjacency bonus. So that's my take.