OK, so someone is writing a city simulator/game, with millions of actors. Fine. They're not very far along yet; there don't seem to be any demo images. Yet they're obsessing on CPU cache management. This seems to be premature optimization.

Their big problem is making a procedural city generator that produces a convincing city at street level. There are lots of floorplan generators and things which produce vaguely reasonable buildings, but nothing good enough to make a video game grade driveable or walkable city down at street level. Unless they crack that problem, their game is going to suck.