The problem is AVIF. I mean I love AVIF (almost as much as JPEG-XL), but it doesn't work with anything except browser web pages, even after all this time.
My only concern with jpeg xl is... how do you know if the encoded file is losslessly compressed or not?
with jpg and png, one is lossless, one is not. But if all the files have a jxl extension, you can't know unless the encoder adds metadata for it, right?