When I think "what do I want for a space opera setting", I answer myself "Traveller, but not so ridiculous." I just need a
little suspension of disbelief, and I haven't had that with Traveller for a long time. Uplifted dogs? Anthropomorphic cat people? Ew.
So I guess put me in the Worked Setting camp, rather than the Generic camp.
I'd need a 3D starmap, for starters. Hell, I'd buy a well-executed map of the stars within 50 or so light years of Earth on it's own. As it is, though, you need to use a computer and software to have any realism there (I've done it).
Also no antigravity or reactionless thrusters, though I have long thought that a warp drive with subwarp capability is an ideal scifi RPG mechanism. 2300AD was the closest thing I ever had to an ideal scifi setting and that's essentially what it used. But it's just too dated. And was too technologically conservative. And the starmap is
wrong almost everywhere you look. Another problem would be keeping up with real-life exoplanets as they are discovered, but I don't think many are within 50y anyway. The Ten Worlds setting for
AV:T is pretty awesome, but too limited in scope.
The idea of a setting in the period of recovery after a Long Night intrigues me, a la The New Era. It would allow tropes such as planets with differing tech levels, ruins, etc. I like the idea of a resurgent polity that is obsessed with "reuniting humanity"- under it's own hegemony, of course- rather like the obsession that the Chinese have with One China. Of course, the worlds that have been on their own for a few hundred years will have different thoughts.
For a setting to have the needed space opera tropes the biggest need is to make interstellar trade (and warfare) viable. To do that you need cheap ground-to-orbit transport, and cheap and timely interstellar transport. Yes, reactionless thrusters are the traditional solution to the former, but I hate them as simply too unrealistic. For the cheap ground-to-orbit there are a lot of other options that are not terribly viable in the foreseeable future but which are at least physically possible. (Cheap fusion powering laser launches, beanstalks, Lofstrom loops, etc.) For the interstellar bit, well, that's why I like warp-with-subwarp. It also lets you easily tool around inside solar systems without reactionless drives instead of turning the setting into just a few radii around inhabited planets, which is what jump drives or gates without reactionless drives do. And most hyperdrives do too. I also like the idea of strategic spacelanes and strategic systems. To do that you need a limit on how far a star drive can take you. Again, 2300AD did this well with its 7.7ly limit, which created such strategic lanes and systems. With such spacelanes you don't need a physically accurate starmap; a subway-style map will do, which is handy.
I've had bits and pieces of a setting like this in my mind for years, but I'll probably never write it down. It presumes that Earth is destroyed and the One China polity is now based out of Mars, which is why recovery has been so slow- there were economic issues, and they were sort of occupied with survival for a while. But I was going to make most world one TL lower than them. The disaster that destroyed Earth (and led to total economic collapse in the setting, since Earth was so dominant) was
AI-instigated, and so true AI is illegal a la Frank Herbert's Dune. This is because with true AI it's hard to avoid a THS-like setting, which isn't very space-operatic. Space opera is iron-willed men with guns, not combat between AI-driven cybershells or transhumans. There could still be some damned capable autonomous drones, though.