This looks like an ideal scenario for torrents, everyone has a copy of packages on the server so seeding will be through the roof, usually on the same network.
No more breaking the world because PyPi/NPM/apt mirror is down.
One tool could support every type of package repository, and then the main mirror will be 'constant' seeds that simply proxy the current locations e.g.:
https://pypi.python.org/whatever-4.3 => torrent://pypi.whatever-4.3
So that you can always get a copy.