The new jpeg spec can be read by legacy decoders and additionally supports ...
* 9-16 bpp int
* fp ("hdr")
* lossless
* alpha (at last!)
The libjpeg already seems to have support for it(?), so how about an im delegate for jpxt?
https://jpeg.org/jpegxt/index.html
https://jpeg.org/jpegxt/software.html
https://github.com/thorfdbg/libjpeg