When your simulation respects actual physics, one solar system is plenty.
I have to say though that I wouldn't be angry at all if there was some officially supported "extended solar system". I'm not even sure the outer planets add-on still works with Orbiter 2016, and considering the wealth of bodies around our humble star, the solar system of orbiter can feel a bit empty at times.
I'm not saying we should have *all* known bodies in there (my CPU would probably just yell at me and then go sulking for a few days).
I'm also quite aware that with all the configs, textures, and now also heightmaps and whatnot involved this isn't a task for the Doctor. And there's quite a few things around on OHM, but it can be a pain to get it all together and working well. Something like an officially approved package would be extremely convenient to have, especially if approval for updating said package would also be centralised.