An initial VR/XR mode is available now in v19.0.4.
The following pen only works in browsers with WebVR/WebXR APIs, and in some cases entering VR mode only works when viewing directly on Codepen rather than embedded here in the forums.
A vr attribute on an <i-scene> element turns it on, and it currently also requires the sibling experimental-webgl attribute.
Under the hood it enables Three.js’ VR mode which supports WebVR and the new experimental WebXR APIs.