The K8s proxy is redirecting from only hosting on GCR to community-owned registries - https://kubernetes.io/blog/2023/03/10/image-registry-redirec...
You can view the code here - https://github.com/kubernetes/registry.k8s.io
But because everyone is already pointing at gcr.io (just like many openfaas users point at docker.io/) - they're having to do a huge campaign to announce the new URL - the same would apply with the author's solution here.
I wrote some automation for hosting (not redirects) in arkade with the OSS registry - Get a TLS-enabled Docker registry in 5 minutes - https://blog.alexellis.io/get-a-tls-enabled-docker-registry-...
The registry is also something you can run on a VM if you so wish, and have act as a pull through cache.
Apart from reliability - GitHub's container registry is the current next best option - but we have to ask ourselves, what happens when they start charging or the outages start to last longer or are more frequent than 1-2 times per week as we've seen in Q1 2023.