This really isn't a nice situation to introduce into a stable release. I think we should have properly handled this similar to how upstream did, which is to only introduce default exchange publishing in the N-1 release, and then introduce default exchange consumers in the N release. That way, if upgraded correctly, all of the publishing side should be publishing default-only at the time of pre-openstack upgrade, which would allow a seamless upgrade of consumer side to default only, once upgraded.
This really isn't a nice situation to introduce into a stable release. I think we should have properly handled this similar to how upstream did, which is to only introduce default exchange publishing in the N-1 release, and then introduce default exchange consumers in the N release. That way, if upgraded correctly, all of the publishing side should be publishing default-only at the time of pre-openstack upgrade, which would allow a seamless upgrade of consumer side to default only, once upgraded.