Hi,
I believe that all comunications should be encrypted by default, no matter
that is public information (tx info), the only exception I would make would
be block packets (to avoid increasing propagation time).

I suggest that Bitcoin Core should generate a public/private key pair and
share the public one with peers.

This could provide privacy and integrity but not autentication.

This way you can impersonate a bitcoin node (active mitm) but you cant just
be passive and record all transactions send or recieved by an IP address.

Today you can just watch for incoming/outgoing transactions to determine
what tx are created in the Node, when you find one you can see the Bitcoin
address inputs and outputs and track that person's bitcoins.

As an example, SSH provides this kind of encryption, althogh Bitcoin Core
should ignore fingerprint changes (caused due to reinstalls).

Please feel free to disqus why this is not needed or why you like this idea.