I think what I had in mind was a client that would run along side your browser and substitute the content of the original website with copies in the backup-network after it detected that the website was down. So you wouldn't actually be connecting to the .com, but it would look like you were.
A distributed backup of the internetz ...
The technical challenge should be, what is the expectation you have of the website. For example if you require the website to be down before you switch to the backup, then a attacker could just change the website to saying something like "This site is being blocked!"
However, a proxy which loads the site from the server and from a stored P2P copy should be possible. And if both differ then you get a icon in the browser which lets you switch between the site and the copy.
I guess what I really meant was P2P webhosting.
I never really looked intro freenet, but at least the wikipedia article sounds very much like what you have in mind.