You could make an argument that we should have AVIF everywhere on the web. But if you want a single image format to be everywhere, I think JPEG-XL is just better suited. AVIF has restrictions on resolutions and number of planes, and doesn't do lossless very well. It's competitive with AVIF on lossy image quality (even though yes, AVIF does seem like it tends to consistently have the advantage there).

AVIF supports a higher resolution at 2^32-1 pixels per dimension, vs JPEG-XL's 2^30-1 pixels. But really it doesn't matter since something is going to impose an arbitrarily smaller limit on either before letting you try to allocate more RAM than any computer can address. Yes, plenty of comparison websites confuse AV1 limits (sometimes AV1 profile limits!) with AVIF limits.

For arbitrary planes, AVIF calls them auxiliary images. Unless you mean encoding non-RGB data to start with like how DNG uses JPEG-XL. At which point you're outside the scope of any standard interpretation of JPEG-XL data.

Image formats goes in era, and there's no need for monoculture. But given we're talking exabytes of data, for this era, the author rightly articulates why AVIF should win. Should JPEGXL2 beat it in the future then it can take over for a decade. We seem to essentially have gone through like 4 formats so far: gif, jpg, PNG and webp. On vector side, SVG has no real competition - it's solid.