And some of us have our own SQL server clusters or rack mounted systems and VM Center for such things. I have a couple of my private hosted server games and it's frankly not an issue. Sure, not a lot of people have access to that, but that doesn't mean it's not possible. They have already done things like this for other games that run fine on just a client PC.
Size isn't the issue - space is cheap.
I'm not talking about hard drive space. Dealing with large databases on a daily basis I know exactly how difficult dealing with a large number of records can be. I'd expect SQL to start to crawl after a few million records without regular and expensive re-indexing. There are already at least 400 billion records just for displaying AND searching the galaxy map. Even using enterprise software on a massive private data center leaves us doingEh, I actually don't think it would be hard at all to run fully on the client. ED isn't really a large scale game asset wise - like No Man's Sky it's mostly procgen with a pretty limited number of actual assets.
I sure hope they aren't using SQL and instead are using some flat file architecture to enable quick searching of documents. My point is, for the scale and level of detail generated by many systems that could become prohibitive without requiring you to do some maintenance (possible but annoying).
For a true offline mode, I would expect each system to be generated on the fly with minimal details stored for your own interactions, if any. I suspect this is how NMS does it and why they delivered such a bare bones system on release. Each refinement of their architecture has enabled more content...much kudos to Hello Games though I'll never play that game.
Ideally, I'd want FDev to release server-client versions of the game which would let us roll our own servers if we have the hardware (or the funds for AWS or somesuch) and then have communities form around those. Not offline, per se, but private online. And the mods....oh the mods...glorious
In the end, I assume that ever since FDev dumped off-line mode they have probably deeply rooted the back-end in a "cloud" based support model. Making that workable for offline would not likely see the ROI they'd need...despite several of us willing to pony up for that.