Your concern is valid but misplaced, there is a reason that we have standards after all. The Library of Congress maintains file format evaluations for the purpose of preservation, and there is an (pretty favorable) entry for JPEG XL [1] as well. Not yet in public, but I'm also working on the very first reimplementation of JPEG XL from scratch and reporting any spec bugs from ISO/IEC 18181 (there are plenty!) and I expect there would be more implementations in the future.

[1] https://www.loc.gov/preservation/digital/formats/fdd/fdd0005...