actually the OBS repository provides an exiv2 package with the required options turned on.
you could also have an exiv2 package in the distro with the formats turned off. and then ship the same source package via fusion and isobmff enabled there. then the user can just replace the exiv2 copy with the fusion one and be done. That’s what openSUSE does with packman.
Technically you can do this, of course, it is much easier.
AFAIK it is against RPM fusion guidelines, though.
Sometimes Guidelines need a revision if there is a very good reason 
This could then also be used to have Mesa with the hardware encoder support turned back on 
Sure, but don’t you think the guidelines are there for very good reasons, too?
We are getting somewhat OT. I meant to provide the background for OP’s observations. In Fedora and neighboring lands (RHEL/EPEL/RPM fusion), we handle legal things and the “boundaries” between different lands in a specific way, which serves us well most of the time, and provides challenges sometimes. That could probably be said about most alternative ways of doing things, too. There’s always at least one way which would be easier in a specific scenario. No reason to change your long tome committment to a generally good way of doing things, though.
I might have a very good idea, why those guidelines might be there. And I also know very well in which cases it might make sense to amend those guidelines and create solutions that will make sure that those 2 packages do not diverge (e.g. lacking security updates) while at the same time giving the users the support for the additional formats.
e.g. for openSUSE it is solved by packman just following the original sources in the distro. and the spec file already having the needed conditionals in place to build it fully functional in packman.
If wanted drop me a PM or contact me on IRC and i can show you the details
What would be the steps to do this?
Yes. And darktable already had a tone mapping module already. Would you suggest discussing sigmoid vs. filmic rgb in a Fedora bugzilla entry?
Next time I know better than offering background on Fedora’s packaging situation here, even if it affects darktable users. If you are really interested in an answer to your question (rather than dragging the discussion further OT from OP’s concern) you find everything in my posts above.
also libavif 
As an example, mlt-freeworld from RPM fusion provides only libmltavformat.so and similar, and the mlt package in Fedora has everything except a few so’s for specific formats. But mlt is a program, and exiv2 is a library … Maybe it could split out parts into separate so’s?
But I’ll mute this thread shortly. Time management …
I’m just trying to get to a solution and avoid the jpg2000 or libavif tangents.
- FR in exiv2 ?
- FR in rpm fusion?
Not sure why you switched to this kinda aggressive tone. you are not the only distribution that has those problems and we actually try to help your users. I just spent a lot of time e.g. to make vkdt and DT work for Fedora users so that they could get up2date packages right after the release.
And the comments about other isobmff enabled packages are actually very relevant for the fedora packaging situation. because right now the packaging is inconsistent as some isobmff related packages are enabled in the distro while others are not.