Update from Ottawa. Please hold off on this. The team has come up with what might be a better idea.
I just created a new story for the Build team to change the mirror download and build scripts to enable us to create and manage per-company, shared import mirrors. This should help insulate most developers from changes in upstream packages.
We recommend building one shared mirror per company per geography. This is a short term band-aid while we figure out our long term build strategy.
The story is
https://storyboard.openstack.org/#!/story/2003288.
Build team, please review and start work on this. Thanks!
brucej