"i have no idea how but..."
yeah ok...
Pretty certain Oculus wouldn't be the format if Stadia went into VR. Google would market Stadia VR individually and push development studios.
Yes, I can imagine a VR headset with a CCU onboard.
But I bet this is very far away. It won't come in the next 5 years at least.
I would think they have a few more priorities at the minute, if it's here to stay though it'll happen at one point.