RE:
Would be nice if there was space to store max volumetric flow (for example) for different nozzles as user fields but then I understand that with 316 bytes available, there is not a lot to work with. What I have in my head is to be able to scan a spool and it loads the profile into prusa slicer automatically.
Playing with the OpenPrintTag generator I filled in as much as I could and there is 63bytes free. But then when I look at the data format specification there is either a lot behind the scenes in the online generator, or some fields that the online generator doesn't give the option to fill in. You may want to look at the discussion about MVF on the github issue if you have any suggestions for implementation.
Or, there is a URL field nominally for the manufacturer's product page. I suppose you could hijack that field for your own web page that your own accessory program scrapes for what ever extra settings you want.
See my (limited) designs on:
Printables - https://www.printables.com/@Sembazuru
Thingiverse - https://www.thingiverse.com/Sembazuru/designs