I'm thinking less about Zynga-like in-browser games, and more like Candy Crush (solo game but it's arguably more fun with others, and def faster/cheaper) and Quiz Up (obv a two person game). For the same user, they'll have different friends lists on SnapChat vs Facebook, and may want to play games more with former vs the latter.

Agree about sticker, but other virtual goods are open. Farmville was rumored to be making $1m a day, and I believe it. Who knows what other iterations we'll see.