Thank you for sharing.
If you have xisf files, this means you have PI, and with PI you can convert them to FITS files easily. Even better, let PI save your files automatically in FITS. I consider this much more a PI issue, than an APP issue to be honest and the solution for a PI user is very easy as you all know.
So I would hardly consider this a priority from an “APP” perspective or a “problem”.
If someone can make the case that xisf is essential due to some special capability (which I haven’t found or seen sofar) or if someone knows that certain camera manufacturers are going to adopt xisf, or capture programs that will only use xisf, then it’s clear xisf should be implemented sooner rather than later off course. (For now, xisf only exists in the PI sphere and I honestly suspect it will stay there)