I think we all knew or know the next logical step is an absolute 'planet' with full neighborhoods and cities, and photo real would be the ultimate, a world based on high rez photography, from either high alt. planes or Sat photos.
Sims 3 has already taken that jump.
It would be interesting to see a 'small' sim based on 'Flight' from long ago done with todays technologies, but with modelled little towns and cars and roads and things, photo real like Flight was.
When that one gentleman did that 'link' system for Flight Simulator that could link into several of the worlds photo systems, like Google Earth, you could literally fly around and see the 'actual' world... I had so much fun flying over France, seeing the country sides.
So creating a world that is high rez for people to view, and possibly making a sim from that, I think would be amazing.
With the right platform and LOD technology, you could make it for both planes, trains, and automobiles....
:d