I think the hardest thing about implementing this is the engine. Everything is procedurally generated (from the same seed), so everytime you enter a system it's created dynamically, and what's not is mostly what Fdev plant into the game - and they can't even do planets filled with volcanic fumaroles / alien ruins / those alien tree like things, just tiny spots here and there.

Each players save game has to include what ships they have and what cargo (inc mats and dats) they're carrying, plus engineered modules. Then add to that each player being able to create bases on planet (plus mining), and this game data has to be saved, even if they stop playing for months at a time but other players can still interact with the base whether the owners online or not...

Unless the base only exists if the owner player enters the system, maybe? Because then the info only has to be saved in the players save file rather than the game files, not sure how that would look in a <supposedly> MMO.