And in case you're wondering: yes, Facebook would be fully aware of the public's possible reluctance to trust Facebook with their finances. While the blockchain would supposedly be "far more centralized" than the likes of bitcoin with 100 or fewer nodes in its payment network, the company would tap outside firms to help run the system. It would charge them licensing fees ($10 million per partner) and roll that into backing the currency with traditional money to keep it stable. You might not experience the roller coaster rides of competing formats.
Facebook has already declined to comment on the rumor. If it's true, though the details suggest Facebook is betting big on the technology. To some extent, it has to. On top of the need to establish trust, this would be a "borderless" payment system that could help offset volatility in some official currencies. A smooth launch might be vital to ensuring healthy uptake, not to mention avoiding trouble with regulators who are already skittish about crypto.