For imposters, the idea solution would be for them to be generated server side per sim - but on a shedule. Adding more for server/sim to do will be a tall order and then coverting 3D to a image.
Could have worked like: Sim generates imposters (maybe at a few LOD level/focal points from each direction North, South, East ,West. Then a client can request the imposter at a LOD level depending on how close the user is to the there current/next (requesting sim) boundary.
Eg - User in Sim A in the centre, looking due East to Sim B - client requests from Sim B's West facing imposter at a mid level LOD. if the user moves east more towards sim b - request West facing imposter a a high level LOD until a point then the Draw distance over laps then client renders the 3D objects form that sim.
Just a idea. not a program or games dev so may have missed a lot of issues there.
Mystic