So Google+ is shutting down over a 10 month period. A security bug provides the excuse to do that, but I expect they were wanting to do that anyway because G+ never went anywhere and never really fit into their business model.

I don't know what sort of demographic the remaining users of Google+ are. Maybe people working at Google and their families? This might be yet another influx into the fediverse.

https://www.blog.google/technology/safety-security/project-strobe