The industry already started throwing out jpeg for heif because jpeg is so woefully inadequate. Most camera brands have heif support now despite heif having horrible patent issues. Jpeg XL provides all the technical benefits without being patent encumbered.

It may or may not be marginal.

For me now, its marginal.

For a past customer, not at all. That customer really cared about delivering image-heavy pages quickly. There was a fairly big difference in customer perception at a timing threshold.

What are you throwing out to use JXL?

The very point of this topic is that JXL is leaving the "early adopter" realm. If your website begins serving JXL assets next month, you'll simply be an adopter.