All the bodies we can land on at the moment are airless, so no sound is possible, of course that will change when we can land on atmospheric bodies. Unplss Odyssey reworks the planet generation system caves are only possible as a crafted object, I am hoping they will change it so we can have proceduraly generated caves and overhangs, and water, it's possible ice I suppose, but tenuous atmosphere doesn't give me much hope for liquid water, now lava I should hope certainly, landing on a lava planet should be fun. There are already plenty of proceduraly generated crash sites, anyone who has spent more than a few minutes driving around a planet surface will have seen them, ruins of course are sadly lacking, here's hoping they will introduce something like that.