It's kind of relevant, but it's probably relevant to half the posts on HN. By this point, it's kind of a cliche to bring it up.

lossless reversible jpeg recompression seems to be a nod to the fact that jpegs aren't going anywhere.

JPEG XL has a non backwards compatible mode too for highest quality/compression and the bitstream can be improved with better encoders in the future.

JPEG XL is allegedly better than WebP, so once browsers get support, seems like it would be the future.

WebP has a bit less features, for example it's only 4:2:0 (which looks great).

Well that kinda depends, 4:2:0 is good enough for video and photo uses, but falls over pretty hard when confronted with synthetic images (e.g. UIs).

WebP is slower and frequently the size benefits are quite small, even non-existent, as you’d expect for an old codec. Anyone concerned about bandwidth or features is probably going to want to support newer formats like HEIC which offer better performance to offset the cost of managing multiple formats.

It's true that JPEG will hang around purely because a lot of software and hardware supports it and they can't all be easily updated. But existing JPEG images can be losslessly (and reversibly) transcoded to JPEG XL and you still get reduced file sizes:

https://cloudinary.com/blog/legacy_and_transition_creating_a...

JPEG XL will be successful for this reason alone.