Provide an integrated (private) docker container registry
For users, this could provide faster pulls and pushes when using custom images. For CircleCi, this could save a lot of ingress/egress, as pushing and pulling custom images probably accounts for a lot of bandwidth.
At least for me, pulling my 500mb custom image from my private registry (hosted in azure) takes a significant portion of the build time, like 5 out of 6 minutes total run time. It would be great to have a registry closer to the test servers. Could be a paid service by the way, I would definitely be willing to pay for a private registry.