Vision and sound covered too, though vision can get better with more res and variable focus. Sound can get better with 3d scanning for custom HRTF's matched to the user's ear shape and body (sound reflecting off shoulders etc.).
Proprioception cannot be fooled. No matter what you do to your vestibular system it's not going to realistically feel like you're in a fighter jet or a race car. It can't even make walking on an omnidirectional treadmill feel like real walking. Galvanic vestibular stimulation is not really a good idea, independent of the fact that it literally sends high voltage electricity through your skull.
Walking on a VR treadmill is actually the opposite example of what you are claiming I believe. It exercises your proprioception without giving you the right vestibular response (except on huge military 12x12ft treadmills and stuff that can accommodate decent amounts of real acceleration from locomotion, I'm assuming you mean consumer "slipmill" type setups where you fully run in place).
Not really. Your proprioception is accurately sensing the same as your vestibular system, which is that you are moving your limbs but you don't have forward momentum because you're not moving. Which is totally fine and indistinguishable from normal in the steady state of walking in one direction at a constant speed as on a regular treadmill, but the illusion falls apart the second you try to turn or change speed, as you'll want to do on a VR treadmill. And it doesn't matter how big the treadmill is, the problem will occur whenever the treadmill changes direction or speed.
If you apply galvanic vestibular stimulation to try to "correct" at least the vestibular sense, you will lose your balance and fall over, because you can't fool physics. Even if you're prevented from falling by a harness it won't feel right. The disagreement between your vestibular and proprioception senses will be uncomfortable.
I mean, yea, earplugs and a blindfold work too, but how do I feel like I'm walking through a pasture with wet dirt between my toes if you cannot simulate the sensory system? That's what people imagine. A home-bound person wants to feel what it is like to skydive, not watch a POV video.
I have seen young people dismiss studies that say that being out in the forest will be beneficial for mental health by saying that for them it's the opposite. Forests gives them high anxiety and being in urban areas will calm them. This included parks.
The key one, the vestibular system, is overridable non-invasively:
Galvanic vestibular stimulation https://www.wikipedia.org/wiki/Galvanic_vestibular_stimulati...
Vision and sound covered too, though vision can get better with more res and variable focus. Sound can get better with 3d scanning for custom HRTF's matched to the user's ear shape and body (sound reflecting off shoulders etc.).