I think a distinction needs to be made between “risk” and “potential inconvenience”.
Given that there are free, open source implementations of the JPEG 2000 decoder, There is no plausible preservation risk. Even if, in 150 years, the contemporary version of ImageMagick has dropped support for JPEG 2000, it would be relatively trivial to spin up an ancient virtual machine and run a 100-year-old version of Linux.
Or, you know, pay an intern to port some old code to whatever modern language they’re using then. Rust, probably.