When it's done.
1) When I can walk around space stations. I don't need a FPS mode but space stations being like the citadel in Mass Effect would suffice.
2) Landable non-urbanized Earth-likes. We're a ways off from that, and I don't ever expect landing on planets with cities, but No Man's Sky is proof this can be done procedurally.
3) Ground Combat Zones. You should be able to use the federal dropship to actually drop marines. The vehicle bay should be able to have APCs and tanks in it.
4) Last but least: more voice acting. Everything should be voice acted, from mission givers, to pirates when they interdict you, etc. The station traffic controllers is a nice start but completing the job would make the game feel a lot less sterile. It doesn't even have to be good voice acting. Some slightly corny voice acting could add some 90s charm.
It's complete when nobody can think of anything more to add to it. It's perfect when there's an offline mode. It's done when it no longer runs.
I mean what everybody means by offline: Not relying on the servers existing forever to be able to play.By offline do you mean a campaign ? Because keeping a whole galaxy updated in offline would be a pain in the *** for them....
The last update before the servers are switched off.