Hmm, interesting! I saw that it's a draft, and didn't investigate further. Maybe it does work indeed on some browsers.

Generally, the compatibility story turned out more fragmented than I expected. Eg, on my phone, Chrome can do AR – but cannot do two camera feeds at once; while Firefox is the exact opposite – no AR but can do both cameras at once, so that you see both front and rear lensed around the black hole properly (in the camera mode).