It wouldn't be the final word on VR API for all eternity. It's a starting point for the spec, which will change as the industry grows.

It doesn't matter much in practice - most people just use Unity or Unreal, which make it easy to target any major VR system. To the credit of these game engines, it's just not that hard to be compatible these days. That's why Oculus has started to use exclusivity contracts to gain an edge.