The "FaceCoin " will someday be a reality. According to many repoprts Mark Zuckerberg's social network would consider creating his own virtual tokens to facilitate paid transactions on his platform that now has some 2 billion user . For this matter Facebook has assembled a team dedicated to the technology of the blockchain. It is directed by David Marcus, former Messenger boss and former president of Paypal.
https://cheddar.com/videos/facebook-plans-to-create-its-own-cryptocurrencyThe team dedicated to blockchain is needed just to keep up with all the latest news, but I don't think they will take any practical steps towards building FB's own blockchain.
IMHO, there is no need for Facebook to launch its coin since they have other methods of payment available that have been successfully used for years.