I don't know if this has been brought up somewhere before, I didn't see anything when searching.
I noticed that there's only a couple bodies in the sol system, in game, that has a hydrosphere listed at all. There are a at least a couple fairly prime examples missing, and a few that are probably less know - Europa and Enceladus are both ice rocks, both effectively 100% ice coverage with the latter being cryovolcanic and having an atmosphere. In fact most of the bodies with volatiles like ice will have at least a trace atmosphere. Pluto has a bunch of ice, most of the outer bodies are likely to be composed at least partially of ice of some sort.
It'd be kinda great if some of that could be added in at some point. It's not critical or anything but it'd make colonizing the sol system a little more interesting for those of us who are reaaaaaally slow about leaving it
e: on top of the ice stuff, some of the planets have more tectonic activity than is generally known. Venus is a great example, because it has a huge number of volcanoes and we're pretty sure some of them are active. Europa's ice acts similar to Earth's crustal plates as well. Mercury is active, and Pluto shows signs of plate activity. Hah, maybe I'm just begging for a full on Sol system pass, as we've learned a lot of new stuff over the last decade. Juno, New Horizons, and others has been a boon.