It seems like Google could have successfully built a "shadow social network" by incrementally integrating their popular services like Gmail, Inbox, Reader, YouTube, Hangouts, and chat into one portal. OTOH, Buzz tried to inject social sharing into Gmail and there was a big user backlash.
I think this is exactly right. It would have been a lot better to organically build a social network across all their products that people actually like to use and comment on. Instead we force them to do things they didn't want to do like real names, but also constantly having to make decisions about what was public or not. It was doomed to failure. I even worked on a project that was a tiny part of Google Plus.
