I'd even go the route to push horizon in kilo version to f22,
even if the
rest of the stack will stay on Juno.
In theory that should work, as it did on my dev platform (using git checkout
and a remote RHOS-6 installation).
Horizon is special, it would be even fine as an upgrade in the
released Fedora since it has no db with state to upgrade.
Swift is the same, it is always backward compatible.
Cheers,
Alan