This is a surprising move from Google; no longer forcing Google+ down everyone's throats. It would strongly suggest that G+ as a service is no longer top priority for Google.

On reflection though, it probably makes sense, Google has used G+ as the glue to track users throughout the search / Gmail / Android / Chrome experiences and to offer great integration as a result. However, the actual G+ service itself is not needed for this integration. By comparison, the rather spooky tracking of a user's movements and tying that to search results makes a lot of sense when targeting adverts.