I do like your ideas.
However, I'd like to point out that Grant only talks about lots/neighborhoods within a world. And that was back before specific functionality within worlds (university buildings, apartment buildings, etc) was in the game. cross-pack compatibility tends to complicate things when it comes to coding.
It's one thing to take a world, add a neighborhood or a few extra lots to it, change the map accordingly and be done. It's a whole different thing to make those changes conditional on a player owning a specific DLC or more.
I would absolutely love if they added new lots and neighborhoods to the worlds though. Especially DSV or Magnolia Promenade.
