Recently I've got an idea on how to solve the multilibs (1) issue on el7+
I will try to forward this suggestion in EPEL land.
Basically there is no need to build the entire repos as i686. There is
enough multilibs packages in base (either the base is rhel or centos)
to build a limited list of packages that really need to be multllibs.
Please have a look at this bug to track RPM Fusion packages that
should be built also as i686.
(1). means that some i686 packages (mostly libraries) should be copied
to the x86_64 repos.
This is usally usefull for compatibilty with 3rd part binary only
applications (steam games, Windows on wine32, binary only 32bit