I, for one, like Lucas' idea.
Eddy Petrișor wrote about doing some sort of user supported thing for snapshot.debian.net, which I was saddened to learn from his post had reached capacity in May.
I think rather than relying on the generosity of random users, the Debian Project should just throw some money at the problem. It's got more than enough. Disk is cheap.
I'd think that with a few fully loaded SR2421's and an Ethernet switch, you'd be laughing.