Multiplanitary Factories would be awesome.
And a way to build a Dyson Sphere ;)
I like Dyson Sphere Program but factorio is vastly superior in regards of gameplay IMHO.
I dare say Factorio is the best game in the genre!
Also not a fan of how hard it is to get around the terrain in the early game. The jet pack needs to come much much sooner in the progression.
Also the random undetectable mini elevation changes messing up your building placements making you unable to load stuff from them to the nearby belt are really really annoying.