In the early plan, there was a bunch of stuff about ship crews (autonomous robots and then later other-player based crews. "Man the turret, Luke". That's yet to materialise.
There's the aforementioned ship-ship FPS module (walk around your ship, other ppl's ships, space stations, repair your hull personally, board and commandeer other vessels etc.. etc..).
Some form of executive control capital ships, which to me sounded like having a pet battlecruiser you could order around, but not fly directly.
Thargoids (alien bad guys) rumoured to turn up "at some point".
That's stuff that was bandied around. What turns up, if and when, can be anywhere on the spectrum.
Planetary landings itself comes in two seasons anyway by accounts, as it's airless planets first, and then atmospheres next.
Given that the lifetime pass is 130 quid, and it looks like it's going to be about 30 quid per-expansion (assuming the base game is purchased), that's equivalent to buying about 4 seasons (both planetary landing sections and whatever the 3rd & 4th is, could be the FPS by then, but don't quote me on it). So, yeah, probably some small amount of clarity on what the other two may be could be useful, although there's plenty of ideas to fit in there, but what/where/when/how who knows.
Hopefully the bobbleheads come back, and apply to more ships than just the sidey in the middle of all this too.