Considering Apple's support and product cycle. You are looking at a Billion devices supporting JPEG XL between now and end of next year. It might be low in percentage, but it is still a substantial number.
could you tell more/point to resources about hw-accel jpegs? does it make a difference for some sort of pipeline/batch operations or 'normal' use too? are there issues with some jpeg features being unsupported? i haven't heard almost anything about this
it's a throughput thing yes, or in my case it's also a desire to not hog the cpu with bulk image processing
features like progressive jpegs and some color spaces aren't supported. I think it could be but it isn't and not sure why
jpegs found in the wild will typically not make use of hardware acceleration or use just it for a subset of the decoding (not sure about the details). browsers didn't bother using hardware acceleration for jpegs just for the images that can be processed fine
so it is meant for jpegs you control rather than jpegs you find on the web. unless you convert them yourself