I don't think this is likely to be the sticking point. The game already has an "asset server" of this sort which puts persistent items into systems (e.g. stations, settlements, megaships). Similarly the P2P networking might mean that you couldn't build one yourself in real-time and have it appear everywhere, but doesn't mean you can't ask for one to be built and then have you and everyone else go to see it later. (You *can* sort of do that with CGs already, after all, it's just that the queue of player-submitted CGs for new stations is really really long)ED would need an asset server or something, where players uploaded what they built and downloaded what other players built.
Without this, you stuff would be gone as soon as you left the instance and not return until you did.
This is probably a relatively costly adition to the game.
Reasons I can think of we don't have one yet:
1) Not a massive amount of gameplay for these things to work with yet other than to say "this is mine".
2) Potential for significant changes to exploration if people can drop landable bases across the galaxy, which might not be wanted. Similar potential for BGS problems if people can just go around adding landable bases to inhabited systems. Especially so if these bases have any facilities whatsoever...
3) Interface to construct a base - which would then probably appear at a Thursday server reset - would be quite complex compared with existing ED interfaces, likely requiring major UI reworks.
4) Frontier already busy with the 10 million other priorities of the player base including "fix all the bugs", "add depth to all the existing gameplay", "implement space legs on populated ELWs" and so on.
Also ....isn't this kind of what the "get yourself a megaship" in Squadrons is going to be? It seems a reasonable starting place for it, with fewer issues around points 2 and 3 than more major constructions, especially surface ones, would have.