With limitations it's entirely possible. However, movement around flying ships, especially in supercruise and during jumps between systems, is probably a technical nightmare to make work, especially in an online multiplayer capacity. I think it's maybe one of the reasons why it has never fully functioned in Star Citizen without issues either, and is a source for a lot of the bugs and jank we see featured in videos here on a regular basis, even when a straight line only supercruise equivalent, which hugely reduces the complexity involved, is used.
For example, when in supercruise in multiplayer some rubber banding can be seen when viewing other ships in supercruise, now realize that the inch or two of screen real estate that you saw rubberbanding is equivalent to a few astronomical units in distance, and yeah, that's going to be a problem for multiple players walking around in the same ship traveling a multiples of c.
A system like that used in Empyrion would work fine for me, entering and leaving ships has to be done when they are at a stop, and if you're not sat down when the ship goes, then you're not going with the ship when it moves - or in the case of Elite, it could prevent take-off to avoid that issue - though having lots of seats/restrainers everywhere inside that act to lock your position to the ship within easy reach could mitigate that too. Having to have a locked position relative to the ship when flying also makes sense from the perspective of flying or driving, where people are generally kept in their seat when the vehicle is moving.
Of course, I'm looking at it from what I see and understand - which isn't much tbh, I'm not sure if the game does any dynamic compression of distance as part of rendering a star system which brings those massive numbers down to something more manageable, which could complicate things too. It looks like the whole volume of space a system is rendered in is to scale, but who knows what programming tricks are used?
Anyway, for me, the whole "it can mostly work, but not without the random possibility of glitching out and ending your game at any time" doesn't cut it when it comes to ship interiors, and until it is 99.9% glitch free, I fine with not having 100% freedom of movement in all cases within ship interiors in Elite.
I also think that Starfield's interiors are basically just building maps that look like spaceship interiors and you're not actually in the volume of space, as it were. Similar to Fleet Carriers, I guess.