I think a lot of people are forgetting something quite important in these discussions.
Let's reflect on the past for just a moment. Eve. They brought in a very limited spacelegs type thing, probably hoping to make more with it. It failed, spectacularly, because in that specific game, it was a pointless waste of developer time. They just didn't know it would be at the time.
Fast forward to today. Star Citizen. It has space legs - in fact the entire 'game' is (supposed to be) centred around this particular fact. Ships, stations, planet ... they've all been designed for something bipedal to walk around in. It isn't an add on - the entire 'game' concept revolves around you being able to walk.
Now lets look at Elite. From the very beginning, you have been stuck in your chair. Nothing in your ship is interactive with your avatar, only your controls. You cannot leave your seat for any reason. If you have VR, you can move around as if you were a camera drone (which can also phase through objects and ship hulls...), but that isn't 'legs' as you can't Do anything. So clearly, the game has never been designed with bipedal motion in mind at any stage - regardless of any promotional videos you might have seen.
And so Frontier would need to ask the question: Is it FINANCIALLY viable for us to spend a LOT of time and effort, which could be going into other more important or desired features, which would be far easier to implement and would take half the time - and thus half the cost - to create a feature that would ALSO require us to add MORE content to the game, make substantial changes to how places like stations and ships work, and may ultimately NOT make us as much money as we would need to cover the initial costs of development?
And I would imagine the answer is no.
Considering the amount of effort poured into the Eve legs system, and the insane amount of work that is well, causing SC to fail completely, the concept of designing a similar system for Elite is, quite simply, staggering.
It would HAVE to be a paid update, and I would imagine it would cost a minimum of £29.99. You have to also consider that, unlike say World of Warcraft or other longstanding games, Elite doesn't really have the same player numbers as these games, which can pump out expansion after expansion every year or so. Also, developing such expansions probably doesn't cost quite as much as such an indepth and complicated update like Spacelegs.
So Frontier would simply have to work out if they could reclaim at least the cost of development for a Spacelegs expansion, and make a profit that would be worthwhile. Breaking even or making just a few percent profits isn't going to be worth the development time, and considering how many people are STILL complaining about buying Horizons, I personally can't see developing Spacelegs being worth their time or money.
It doesn't matter if it would make the game 'better' or 'fun' - if it isn't going to benefit shareholder coffers, it isn't going to happen.