What's the benefit in changing to be compatible with YUM as opposed
to stickin with current alogorithm ?
If a user migrates from RHEL 7 to the next version of RHEL (or CentOS),
there will be continuity in used algorithm and history db checksums.
It's important to some enterprise customers to keep the history db in a good shape.
Fedora users don't care about that much in general.


Surely if we don't change it, even fewer users will notice that DNF's
behaviour is different from YUM's, since DNF has been the default for
many releases now.

I could understand the motiviation to stay compatible with YUM if we
were only just about to switch Fedora from YUM to DNF, but time is
way in the past now. Shouldn't we optimize for the fact that DNF is
the more widely deployed & used tool, and thus not worry about
YUM compatibility in respect of the history DB ?
Unfortunately RHEL knows nothing about DNF yet
and it's YUM compatibility what matters.