Seems to be just a rumor, but one that I hope is true. I also hope they use it as an opportunity to finally fix the longstanding ugly wart of having Live Photos be a separate .MOV file sitting alongside the HEIC file. JPEG XL is a container format so it should be possible to include the MOV as a separate box alongside the jxlc data and exif metadata. Of course, HEIF had the same capability and they still didn’t use it.