To address sprawl, the Atomic Age could enable a third building in quarters
Obviously this would need a ton of balancing work, but I think it would make city planning a bit more flexible when the warehouse and ageless building pile up. I think Unique quarters would not be able to add a third buildings.
I also think this could restricted to another tier of upgrading cities, maybe called a metropolis. Modern Japan feels like a natural civ to give these bonuses around this feature.
Perhaps a tech in the Modern Age would unlock a small version of this with a third building slot unlocking on the city center with a tech or civic.
Building limit could be another mechanic to allow for tall playstyles, save valuable rural tiles, and avoid more buildings like the rail station that require an entire quarter. Perhaps this could even be worked into the Modern Age in some ways too.