Copr architecture doesn't cover mirroring; every package is stored on one (backend) machine. It would be nice to have some mirrors, so even project which require the repositories/networking 100% online can depend on copr.
No customer requested this, and the coprbe.devel.redhat.com appears to be relatively reliable after the years of service. In Fedora Copr we already use CDN (AWS CloudFront). Closing for low priority.