I would like to see them update the little buildings and ships which appear around a colonised planet also. At the moment the ships aren't even ships they look like 2d sprites which circle station to station.
Honestly I personally don't care since I end up turning them off anyways.
Although new textures for each of the planets would be nice. However, more planetary sizes would be a good start. Perhaps new default planetary types is a also a good start, if devs need ideas look at the distant stars or any mod that has brand new planets.
Although this shouldn't be priority. Get the other races in first.