Here’s what I think the integration of Gmail and G+ messaging is really about: Making communications about people and permissions, rather than possession of contact info.
I get behind this - 100%. In today's world, email and phone numbers are used for identity and are also far too public. In addition, current privacy, security and data collection practices completely revolve around using these identity mechanisms.
In a new identity, I would have control over what gets shared, with whom and a completely secure new identity that wouldn't get stolen even if someone knows me email-id.