Neighborhoods with tones of fake buildings looks dead...

I don't think rabbit holes are good idea. Had them in Sims 3, never loved them. If my Sims doing something, I want to see it.

What would be great is to give shells some animations and let npcs to go in and out of them. Maybe even let the game to assign homeless sims to shell homes, like it's their house, they live there, see how they go out of their home and go for a jog.