There's been a few threads on these forums about JXL but no real feedback from Serif on their plans other than an answer that it might happen some day.
I really do think Serif should consider JXL seriously and be a first mover in regards to this format. The reasons for supporting JPEG XL is many, a new actually great format for >8bit final export, possibility of lossless quality, transparent conversion to JPEG for compatibility, better compression and more. Some sources: source 1, source 2.
The reason I think Serif should be a first mover in regards to this format is that no new format will ever get the chance at dethroning JPEG from it's role if nobody ever implements it in their software. Browsers do support JPEG XL (JXL) but the enablement is hidden behind browser flags currently, partly because nothing else supports JPEG XL at this time.