this sounds insane. but im not familiar with all the concepts. it seems that now instead of alice and bob exposing their real keys, you have node a, b, c and d

this sounds insane. but im not familiar with all the concepts. it seems that now instead of alice and bob exposing their real keys, you have node a, b, c and d exposing theirs during bob handshake... which will lead to sociopath nodes that wont be part of this, but rely on nodes that accepts it for them. also, if the message is encrypted, why not use a "torrent" of all the messages being shared and discarded after a while (no need for offline messages anyway) and each node decrypts its own as they please but relay all of them in the same stream? no way to know who could decode it. and it was delivered to everyone. much like a bitcoin transaction, but without the metadata. it would probably be vulnerable to a dos by flooding it with bogus, expensive to try to read, requests... but will be the most reliable and private you can get