I'm just reading through the wikipedia page on this for the first time.
Does JPEG XL allow encoders to switch between the DCT and modular modes on a per-macroblock basis, or is it just on a per-channel basis?
If it's the former then I can see this offering a lot of utility over other image formats because you'd be able to disable the DCT on high-contrast macroblocks and finally be done with all those god-awful "checkerboard" artifacts around the edges of objects.
But if it's merely on a per-channel basis then I'm not sure I see what the point of this is since I can already use a different format when I need lossless encoding; If anything JXL would become an annoyance because I can't tell if a JXL image is lossless or not based on the file's extension.