Gave it a try. I like deeper integration with social services, but I'm not too excited that it's primarily just a shortcut to the app's chat feature (which I don't really use, honestly). I was hoping that it would let me send signed/encrypted tweets, or Gmail messages right on the page. Is that within the scope of the project, or is everything meant to happen from within the app?
For things like encrypting emails inline, we could explore it but I'm not convinced it's a good use case: To get all the benefits of Keybase (identity verification, key/device provisioning, improved encryption over PGP), the recipients would also need to have Keybase installed which means you could just use Keybase Chat instead.
[0] https://twitter.com/shazow/status/605748307688890368, https://github.com/Lukasa/entweet