The advantage is increased battery life and performance, which is way more important to most end users than any of the advantages I've seen for JXL. People are

The advantage is increased battery life and performance, which is way more important to most end users than any of the advantages I've seen for JXL. People are not pixel-peeping different images to compare quality, they are annoyed when their battery dies. As to hardware adding support for JXL, that seems extremely unlikely: image decoding is less impactful than video decoding, and the cost of adding custom decoding silicon to a chip is very high, as is adding support to software for that hardware. Being able to piggy-back on the work already done for video meaning you get that stuff for free makes it way more viable. AV1 decoding is already out there in virtually every new device, and rolling out hardware support is very slow, it's massively ahead in that respect.