Personally, I would love to see something like this come into being ...
I just couldn't see it even being playable on any sort of large scale unless you forced it to 'real-time', and provided some sort of 'quantum-jump-handwavium-movement' to get to other planetary orbits. Like a single beacon point in each planets orbit you have to maneuver within 10km to use or something ... press the button, *BANG*, you come out at the Mars beacon ...
That would rid you of the 5+ month wait to get to Mars ... and you could make it rough on the players by only physically moving them ... their delta-v remain the same relative to the Sun on exit as they had on entry ... you don't have a ship capable of making the velocity change, well, just wave 'bye' as you watch Mars get smaller and smaller ... and only allow jumps from one planetary orbit to the next ... to get to Saturn, you'd have to go through the Mars, asteroid belt, Jupiter, then Saturn ... maneuvering to the next beacon on the way ...
This would still require a lot of the orbital maneuvering skills needed for Orbiter now ... but would let people get all over the solar system within a few days real-time and actually cooperate.
I have this vision in my head of people setting up refueling stations, asteroid mining operations, freighter services, etc .... Just an idea ....
Yeah, it wouldn't exactly be Orbiter anymore, but it would/could/should contain as much of it as possible.
(I used to be hooked on 'Eve-online' ... got disenchanted with it ... not enough realism ... been trying to think of a way for quite a while to get the economy/cooperative nature of the MMOG, and have the realism and patience required in Orbiter. Someday ... hopefully ...)