I considered both these points when I was composing my answer but came to the conclusion that this is true for basically any encryption strategy, if I've transmitted contents signed with your public key then when your private key becomes known so does the contents.
Even when you manage to keep the key secret I can't revoke your access to the material or prevent you re-transmitting it to others.
True, but if there's one shared key for each page, the chances of that key getting loose are higher. There are alsomethods of encrypting a message where you can specify multiple recipients (i.e. multiple keys), letting you remove one key without affecting the viewership of the page for people with the other keys.
It's a hard problem, and this is certainly a novel solution to that problem, but I still don't really see myself using it.
