I was not able to express properly - sorry about that. You generate one key pair for one shared item. I'm talking about multiple key pairs for each shared item

I was not able to express properly - sorry about that. You generate one key pair for one shared item. I'm talking about multiple key pairs for each shared item, so that I can give access to individual users for the same data and revoke them when necessary. Fundamentally if you don't have that, then your case is trivially solved by a private bittorrrent tracker. This is the fundamental difference between things like Quilt and bittorrrent.