I think it's a good plan to have backups but please do keep in mind that "doom is imminent" may be a self fulfilling prophecy, if everybody starts apt-mirroring in bulk.

Right now, the maintenance is sparse and it mostly relies on peoples good will and free time, so putting unnecessary strain on the servers might bring the end a day earlier.

I'm not suggesting not to backup. I'm just suggesting that one person is charged with each asset and he does the backup in the most light way possible (delays between successive downloads, speed capping etc).

I'd also suggest to change the title to something less panic-inducing, like

Coordinated infrastructure backup team - come to help.