Most major break throughs started from a very specific problem, that was addressed, got some market traction, and then refined over time.
Large up front investment without testing the market has been done before, but I can't really think of a single recent example where it went well.
Maybe perhaps SpaceX, but I'm not really familiar with their founding story and costs associated. But also consider that one is literally launching rockets into space, the other is creating a VR/AR headset.
Launching a single rocket costs millions! Buying this or any AR/VR headset will ultimately cost $1,000. Hence I don't see why you need $2B to get this off the ground.
And if they are having a problem shrinking the tech, well then it's not a real product. Because they aren't pitching here is a refrigerator sized computer and a headset, they are pitching here is a headset, so if you haven't shrunk it, then you really haven't built the MVP you were looking far as portability and comfort I'm sure are part of the essential requirements for this product.