three.js r87 will bring a optimized handling of scene.background and should work nicely in VR.

https://github.com/mrdoob/three.js/blob/dev/src/renderers/webgl/WebGLBackground.js#L26-L108

I think a-frame should add support for this. Right now I see people creating spheres and adding them to the scene which is not the most optimal way of doing it.

Maybe <a-background> as a component could also work. That way one could add more logic to it like converting equirectangular to cubemaps (using CubeCamera) automatically.