Also, a separate domain, wikipediap2p.org, not (obviously) affiliated with wikipedia.org. If it were p2p.wikipedia.org, it would be fine for me.

It says on the page: "This is an unofficial extension and not endorsed by Wikipedia in any way, it's just an implementation of latest web-technologies towards sharing of knowelege."

I think changing the links to point to the cache instead of the original server needs that permission.