PeerCDN tried this and was acqui-hired by Yahoo in 2013 and Peer5 did this for video but was acqui-hired by Microsoft. What about P2P CDN didn't work before?
For example, to intercept network requests to serve them from the peer-to-peer network, a <![CDATA[ tag had to be inserted into the <head> of the document to block rendering of the subsequent document. Then, once the document had finished downloading, the page HTML was manually rendered so all assets (eg JS, CSS, images, etc tags) could be loaded via JS instead of the browser natively. This was both slow and resulted in empty white pages on load. Now? We have the Service Worker API. (https://developer.mozilla.org/en-US/docs/Web/API/Service_Wor...)
I'm not as familiar with Peer5's tech stack, so I can't speak there. But hi Shachar!