Regarding these two questions:

Are there any concerns about such change?
I believe that >90% users wouldn't notice anything as it's related to the history database only.
  
On Wed, Jul 18, 2018 at 10:01 AM Igor Gnatenko <ignatenkobrain@fedoraproject.org> wrote:
Since we've changed the database entirely, what's the point of keeping same algorithm for calculating checksum?

On Wed, Jul 18, 2018 at 9:34 AM Daniel P. Berrangé <berrange@redhat.com> wrote:
What's the benefit in changing to be compatible with YUM as opposed
to stickin with current alogorithm ?
 
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 ?

It is true that going forward in the Fedora world it matters less.  It is more of an impact for yum-3 compatibility as yum4/dnf is being considered in the RHEL7/CentOS7 userspace environments as described at https://blog.centos.org/2018/04/yum4-dnf-for-centos-7-updates/

Currently yum version 3 and what the proof-of-concept project is calling yum4 work very well together side by side.  Users can safely switch back and forth.  The major problem is yum/dnf histories being different and the rpmdb checksum difference is a blocker for resolving the history compatibility.

So think of this as an effort to bring package management parity between Fedora, RHEL 7, & CentOS7, as the latter two still have a long life ahead of them.

Hope that helps,
Terry