[whyrusleeping]

ipfs dev here! This is indeed possible, you will be able to listen on announcements (provider messages) of hashes that are near your nodes peerID within the kademlia metric space. To get a complete picture of all hashes on the network, you would need to ensure your nodes had reasonable coverage over a good portion of the keyspace (enough that the K closest peers calls for any hash would return at least one of your nodes).

I really want to build something like this, just haven't had the time to do so.