Basically more ways that different buildings can interact without interacting like houses with fences having connected fences and more alleyways with trash cans in them and decorative stuff like that, that could possibly be used in clever ways.
Incredibly difficult with the way mapgen works right now. Essentially buildings have to be designed with this in mind, and with the knowledge of where they will be in relation to each other, otherwise there has to be a lot of context aware stuff going on that’s currently not.
perhaphs treat them like a single structure but have both have own icon on map
That would be doable as part of the overmap special system, but to fit it into the current houses would be difficult.