Terraforming, Ringworlds, sphereworlds(Dyson spheres) would be great but the current technology tree suggests only incremental advances as if like a WW2 game. Of course, another expansion could change every thing.
Also, please, Orbital Rings(like in The Culture novels and others), Orbital Spheres, and ships as population centers like in The Culture. Ships and Orbital Rings are their greatest percentages of population centers. Planets are like back country villages, research stations, and nature preserves.
See my signature below. Lol.
Only as long as they can be disabled, please. I've never liked "super projects" in space strategy games.
"Evil is easy, and has infinite forms." -- Pascal