I've decided. I'm going to do a setting for SC3 based on the Solar System as it existed before the coming disaster that caused the Diaspora was dicovered. This may include the extrasolar colony in Alpha Centauri, but not the other colony ships, as they had not yet established themselves by this time. I am tempted to only refer to the extrasolar colonies in passing though. Setting up a viable Tech Level 8 society will be job enough.
I will use the random tables in SC3 to an extent - we know where the planets and moons of the Solar system are, their natural Conditions, and that Earth will be the most heavily populated world, but the details may be best determined randomly. It may be that Mars is not a popular place, and that Europa or Ceres are far more heavily settled. using an element of random generation will result in my having to come up with reasons *why*, which is always more interesting than doing the expected.
There should also be a heavy contingent of orbitals and stations, which are not there at this time. The cheap energy of fusion coupled with the cheap resources of in-system space make such a development likely.
Politically, the UN and it's member nations will be the prototype of the Leagues of the Cluster, with their member worlds. The UN does not rule worlds, but it regulates the space between them. A closer model for the Leagues than the current UN would be an amalgam of NATO and the EU, but the UN may grow into that - or absorb these entities - by the time of the setting, so I will go that way.
One thing I can do is add in a bioengineered solution for calcium loss in zero g. I have always assumed it, but it's best to place it front and center for this setting.
This would not be at all post-human. TL 8 bioscience is pretty much limited to non-visible changes in humanity. There will be early uplifts, and simple - but still sapient - robots, but the setting will be mostly human.
Average PSI will be 0, not the current -2, or the Cluster's 2. This is a result of early bioengineering, and the fact that the people sent to the Cluster later would not only be of a somewhat later generation, but be their best and brightest.
This culture will be shattered by the news of the impending disaster, and the culture that girds up its loins and sends ship after ship out into the unknown in faint hope of some of them surviving will be a different beast altogether - more like the US Home Front in WW II. This may be remembered by those refugees as a golden age, fraught with both danger and opportunity.
Any ideas you'd like to see implemented?