Quick - call a sociologist
Speaking as one who runs dovecot and prosody for imap and xmpp respectively, some kind of combination seems a good idea, providing OTR etc can be part of the mix. Thunderbird's chat, for example, doesn't allow OTR. The way we use imap and xmpp is exactly as described in the article - at times, chat-like activity takes place over email. Chat (pidgin client) used as a file transfer mechanism also takes issues away from mail.
But I can't help thinking that the real research should be into why people herd themselves towards closed ecosystems. That's the non-technical issue that seems to need solving.