With a Rift S, I played the whole of HL:Alyx sat down, using the normal FPS movement method rather than the click-to-move method. I'm not entirely sure why I would need to stand up to use space-legs... not as if you are actually going to be walking anywhere. Much like switching to an xbox controller for driving the SRV, I cannot see picking up the Rift controllers when switching to legs being a particular challenge. I already do exactly that when I exit Elite to play something else.
While typing this it has occurred to me that I have very limited experience with how any other VR hardware works - I know my Rift S and that's it - so while I don't believe the Rift S would present too much of a challenge to integrate, maybe some of the others would?
I think what M4RTH4 is getting at is that: (A) They'd need to add motion controller support at minimum to match market expectations, & (B) There's an expectation of being able to play character gameplay via standing / roomscale play.
You can certainly then chose to play seated, but the above need to be accommodated as a rule.
Odyssey complicates things by having that transition between vehicles and characters. Accommodating a range of norms / preferences isn't insurmountable at all. It's just dev. (More dev than they've had to do to date etc).
In NMS (the most comparable game to ED on functionality), they went to town on the VR support to soften the transition between ship and character gameplay. They added virtual joysticks etc, so that people could control both ship & character with one control scheme (motion controllers). They fudged the standing play a bit (the UI doesn't rotate if you turn your body in roomscale), but ultimately it's pretty functional. Odyssey would probably require FDev to noodle around with their own solutions for smoothing out that experience where possible. For a high end release.