Think Egypt, Syria, China: countries where large-scale keyword filtering and MITM attacks are common, and the infrastructure is owned by the opponent.
What's needed in those cases isn't peer-to-peer encryption, but peer-to-service (and service-to-peer) encryption: tweets encrypted on the device, sent, and decrypted on Twitter's servers; timelines sent encrypted, and decrypted client-side.
Twitter still gets plaintext, but intermediaries can't trace/target pseudonymous users (or filter content).
This could be a real edge for Twitter in countries (China) where they're losing ground to monitored/censored clones (Weibo).
tl;dr: They're probably building Tor, not Skype/BBM.
What's needed in those cases isn't peer-to-peer encryption, but peer-to-service (and service-to-peer) encryption: tweets encrypted on the device, sent, and decrypted on Twitter's servers; timelines sent encrypted, and decrypted client-side.
Twitter still gets plaintext, but intermediaries can't trace/target pseudonymous users (or filter content).
This could be a real edge for Twitter in countries (China) where they're losing ground to monitored/censored clones (Weibo).
tl;dr: They're probably building Tor, not Skype/BBM.