You can fork the registry code [1]. We work in a regulated industry (healthcare) and need excellent access controls and auditing/logging. Forking the registry and rolling our own is possible, but not something we want to spend time on. So we looked around for private registries. We went with Quay [2] and have been really happy. They're responsive, performant, and on top of enterprise-level requirements.

[1] http://blog.docker.io/2013/07/how-to-use-your-own-registry/ [2] https://quay.io/