Sure, I use j2k (and djvu) every day. They're one possible format to transfer archived files and scans to, although being business, PDF/A is preferred over any raw image format in this group.

I'm just saying that major public formats don't just disappear, even if they become inconvenient to use; most major obsolete undocumented formats are still usable in some inconvenient way or another.

That's not how kitchen sink libraries work, though; they support a lot of obscure and dead formats with known security problems in the implementation, but none of them are enabled by default. If you want to make a tool that's an everything-to-anything, you turn on all the compile options, and if you make it public, hopefully point out that here there be dragons.

Some binary-only remains might very well require virtualization in the future, the way accessing and converting old Pagemaker files does, but that's something retro enthusiasts seem to relish.

The good thing about dead formats is that they're frozen where they stood, instead of having dozens of proprietary and incompatible variations. (Cough, anything IFF-based.) Unless they already made it that far before dying, like PCX. It's the proprietary ones that really painfully disappear, like exclusive Adobe-only formats.

I doubt JPEG XL (or XR or maybe XT/XS, or any other also-rans) will end up in that situation, since they're incorporated into the main Swiss army knife libraries, so some utility or another will be around to deal with them as long as the C language survives. It may not be convenient, let alone integrated into your favorite tools, but nor are most dead formats.