[jmull]

> Why single out JPEG XL?

Hopefully it isn't singled out, and any prospective support for a new image format gets the same scrutiny.

The question is different for any image format that is already supported, because removing it breaks the web to the extent the format is being used. That's really an argument to be particularly careful about adding support for a new format: once it is widely available for a while it is almost impossible to remove. This is a one-way decision (unless it's barely used, in which case there wasn't a good reason to add it in the first place).