I haven't posted anything on Google+ is well over a year. I don't think people moving to Google+ from FB. And, I'm sure Google+ is not the next big social network.
I hope that the next social network will be real life and that online services will go back to what those things used to be: websites that do one thing good (see Flickr) rather than trying to buy our mortal souls. Or giving me (us?) the feeling this is is what they're trying to do.