I completely agree with you on the human aspect, but what precisely would you want to see with regard to "social aspects". Please be as specific as you can. What tools and options would you require to have in order to have this work for you?
Specifically, I think it is important to reduce metagame fragmentation of the online community. This primarily means creating a system which pulls people together as much as possible while striking a meaningful balance between group and solo play. Social aspects of MMOs do not necessarily mean group play. Solo players are there too and they are a big part of the social equation just by being online.
This can be achieved in sandbox games easier than heavily scripted ones. For example, for players who are wary of unsavoury characters ruining their hard earned credit balance via piracy and wanton violence, instead of giving them a way out via the private/solo group, you give them ingame tools to minimize but not eliminate completely, the chance of undesired encounters happening.
This could be anything from stealth ship skins in place of more protective armor, juiced up sensors, expensive and rare police-grade scanners available only to reputable commanders to punch through the no-transponder camouflage and expose potential harassers early on, frame shift cooling systems or stabilizers for faster getaways, even smart mines you drop behind your ship to discourage direct pursuit. The options are limited only by developer imagination.
What you achieve is encouraging meaningful player choices and above all,
direct and indirect interaction. Do I outfit my hauler with extra cargo space, or would that engine booster come more in handy? So I invest in the military-grade stealth skin for my ship so that it is harder to detect in sublight? Or a thicker armor? What about a stealth frame shift drive so that I cannot be seen as far away in superluminal? Or could I use a more fuel efficient one so I save money on my trade runs?
Then there is tweaking the simulation. Is that station camped? Well, why have just one station in the system - the economy is system-wide, there could be plenty of stations. Just go to another one. Is the number of pirate attacks on the rise recently in a system? Is that system lawful? Well, the police get there in larger numbers, with bigger ships. Patrols get more frequent. Player and NPC bounty hunters are pointed to the system. And pirates have to leave someplace else.
On the other hand, you give the hunters tools for their trade. Better scanners, faster engines, tailgating and hyperspace trailing we know will be in the game. And you balance it all so that it has a clear purpose.
You enable players to make ingame choices which matter and which work. You also enable players to make mistakes and suffer the consequences. You allow players to take risks and reap the rewards. You allow them to fail. Failure is a big part of success. Without the possibility of failure, success means little.
But the bottom line is, you do it all in the game. Someone wants to play solo, they go to fringe systems where they will hardly meet anyone ever. And if they do chance upon someone, they just deck their ship out so it suits their desires not to have to interact with other players.
But not quite 100%. For people who 100% do not ever want to see another human player in that galaxy, there is solo offline, which is separate from online and you cannot transfer between the two modes.
Keep the game menus out of the game as much as possible, that's the thing. Give freedom to the players to play as they want, but together, in one persistent world. Instead of indulging player segregation, create gameplay out of it. That's how I would go about it.