I'd say procedural cities are one of the easier things they have on their to-do list! Although roads would be very tricky.
None of this stuff is tricky if the game has time to go away and think about it but it has to be calculating stuff at 60fps on top of everything else it's doing, so it'll tend be stuff you can create just by saying what_building_is_at(x,y,seed) rather than being something where it works out an elaborate layout taking local factors into consideration. Although what_building_is_at(x,y,seed) could be as clever as you want it to be.
None of this stuff is tricky if the game has time to go away and think about it but it has to be calculating stuff at 60fps on top of everything else it's doing, so it'll tend be stuff you can create just by saying what_building_is_at(x,y,seed) rather than being something where it works out an elaborate layout taking local factors into consideration. Although what_building_is_at(x,y,seed) could be as clever as you want it to be.