Not a VR expert, but it seems to be about same thing for OpenXR+Vulkan as A-frame is for WebXR+WebGL. Minimalist 3D engine with simple API wrapping much more complex lower level APIs, "reducing number of things which can be done in exchange for making some things easy to do with it". Native, not web app.

OpenXR is "Vulkan for VR" by the way, every major HMD vendors runtime supports it. Though only SteamVR supports Linux, and there's mess with support of advanced tech like asynchronous reprojection, I hope Monado which is "Mesa for VR" will succeed. And Firefox gets WebXR.