Would there be any interest in a service or software that allows hosters to automatically move content and direct requests for content to a set of servers hosted at various datacenters.

I know this sounds a lot like CDN's but the big difference would be that no changes would have to be made to the site content and content would be moved only when the origin site gets a lot of traffic.

Web hosters could use this to make all their offers of "unlimited" bandwidth and when/if any sites start reaching capacity, they would automatically be handled by the overflow servers.