Their decision is schizophrenic: the JPEG XL format is a combination of two technologies: PIK (developed by Google) and FLIF (developed by Cloudinary) -
one of them developed by Google. It is entirely sensible for them to reverse their decision, which came
before Safari announced the format would be supported.
Adobe is already supporting the format, and many image editors / browsers are including it.
Finally, adding a WASM polyfil to your website would still yield many benefits, enough to outweigh not-100%-yet-support-by-browsers.