The problem with XL is that it has way too many features. HDR, for example. Firefox doesn’t support HDR at all, Chrome added HDR image (not video) support just late last year. And that’s just one feature of XL… Even if both Google and Mozilla will start actively working on support we won’t see anything useful for a few years. And then how do you even create images in the first place?

It doesn’t work anywhere because full support requires so much stuff that no browser can be compatible.