I doubt it. Distrust in Facebook is as higher than ever. The people on the site are not going to be interested in Cryptocurrency, much less one that Facebook offers. Unless they replace the gold tokens in their gaming space or the stars on the livestreams with globalcoin, it's not going to take off.
If they make a system that for all intents and purposes is just like say PayPal for the average user.
Meaning no nonsense with keys and Wallets and what have you, I could see it happening.
You've got a point there. Whether or not people use it will be another story...