BIP70 only supports request. What about send?
There's no good way to embed a message in a bitcoin transaction. Sorry. Why do you require that?
BIP70 also requires request party has a CA and url. A lot of p2p won't have those.
It doesn't require a SSL certificate, it's extensible so you could use GPG identities, but trust networks aren't very well established.
Perhaps if you told us what exactly you were trying to do, we could be more helpful?