Earlier quoted context omitted.
Is there some precedent of this from the past? I haven't heard of this "rule".
The social platform where young people spent most of their time kept changing in the past - I think it went something like this: Netlog > Facebook > Instagram > TikTok. There have been lots of other social networks that have been popular at some point and then eventually declined or even disappeared: Google+, Snapchat, Vine, StudiVZ (German speaking countries), the list goes on...
I just don't see that applying to any of those, certainly not G+ :)