If this is a sandbox then plenty of scope for maybe colonization or exploration and expansion packs and other content as u go along
Well this is a big problem that Mount and Blade had; in the initial version there was very little to actually
do with the sandbox.
It's telling that the major mods and expansions for M&B all added two things to the game:
1) The ability to form your own kingdom
2) Strong, neutral themed armies that were distinct to the main factions.
I'm kind of taking it for granted that at some point planetary conquest will be an endgame option in Starfarer (although not necessarily; there are plenty of directions the game can be taken where it wouldn't feel like it was missing). I'm also hoping that there will be some form of endgame antagonist challenge that will be optional but also fun and rewarding to go after and alien incursions are a nice easy way to do that (but again, hardly the only option)