I remember signing up in 2005 because I was taking German for my future trip to the World Cup (pointless as 95%+ will reply in English (edit), unlike those darn French!).
As it grew in size and popularity, the limited nature of it really made those that couldn't get in jealous. I remember all the kids screaming about the feed when it went live, how they'd leave. Then once it opened to everyone, they'd leave then.
WhatsApp seems to be the new kid's playground, so facebook buying it was a smart move.
There will be another. Hell, maybe I'll make it :-)
Dropped out of my (still better IMO) Telegram style program after worrying about N$A fallout.