traffic analysis?

[sneak]

What's to prevent a p2p node from logging all of the historical communications patterns from identity to identity, and reconstructing the social graph to link known identities to pseudonymous keys?

If I understand the docs correctly, this is to be used for an email/DM type of app, where the identity's key could be used to encrypt a message (sort of like Steem's "memo key"), yes? Is it a known issue that such encrypted messages would have unencrypted metadata and expose traffic frequency and source/dest?