That sounds like a good preference: “Should Photostructure render previews and JPEGs, AVIFs, or both” (and then an explanation of why one might choose one or the other, and a warning more drive space will be used but streaming could be more pleasant).
For those of us that don’t use Apple products (my wife and I just use Windows PCs and Samsung phones and tablets), I wouldn’t mind an “I don’t care about Mobile Safari” option that uses newer file formats only supported by Chrome and Firefox.
Someone from the images infra team at Facebook has a lot of good feedback about JPEG XL as well:
After spending the last 5 months investigating and evaluating JPEG XL from both a performance and quality point of view, it’s our opinion that JPEG XL has the most potential of the new generation of image formats that are trying to succeed JPEG.
Recent news about the jxl library being developed in public now:
(There are still a couple blockers before jxl is in sharp: but I could do reencoding with an external tool, similar to how I handle HEIF. There are serious performance downsides to that approach, though)