Ships: potentially even containing illagers. Could be found randomly in and around systems and shoot back. Not as hard as space whales please.
Pirates: basically ships which if within about 4000 blocks when you mention flying crates to anyone have a 33-66% chance of intercepting the transmission and start coming towards you. Not that hard to fight but makes game interesting.
Potentially tanks or walkers or even speeders on planets which have a outpost or 2 that is about 100 block circle of its own type of land. During night has 5% chance of going after nearest level 7+ player (same with above actually too) and have mediocre little vehicles to good vehicles depending on level (possibly). For fully claimed planets could be at the edge of the -ost’s
I think this would make it interesting in the game and add both slightly more challenge, and ways to get resources.