What would make you build Neighborhoods? Or perhaps more Neighborhoods. You can assume that the change would go along with some late game balancing.
A third construction option in addition to shopping mall and food mart: a police station that acts like the counterspy mission and protects the neighbourhood and adjacent districts
I do like these. The latter in particular builds on the whole tall thing well.The option I always thought made the most sense is neighborhoods should increase the yields of specialists - either by 1 of the appropriate yield in all districts in that city, or by the district adjacency value for districts adjacent to the neighborhood.
more use of high pop
I'd probably also add "be able to build them sooner" as an option as well. Right now, a "neighborhood" really means suburb. However, neighborhoods have existed probably since cities have.
Seeing as Civ6 generally lacks +% bonuses, I think neighborhoods could fill that gap. Seeing as you'd only build them in big cities as it is right now, it'd make sense to increase housing AND get a nice +% yield bonus on top of that. If that were the case, the housing would just be a bonus on top and the +% bonus would be the main draw.
I'd probably also add "be able to build them sooner" as an option as well. Right now, a "neighborhood" really means suburb. However, neighborhoods have existed probably since cities have. I doubt Gilgamesh lived next to beggars and the immediate area around him would have reflected that, as an example. Anyways, from a functional POV, being able to build them sooner would make going tall more viable since it would be a way to avoid the housing crunch most civs face in the early-mid game (late classical) AND would actually help a "tall" civ catch up by maximizing the yields from those currently "extra" pop points that tall civs have.
How vulg- oh wait, you meant slots. Oops...Buff specialists. Increase number of specialist sluts. Done.