They could have a roadmap to slowly distribute initial stake over the time, for example (if used PoS, which I think the most probable plan). And the case would

They could have a roadmap to slowly distribute initial stake over the time, for example (if used PoS, which I think the most probable plan). And the case would be not to own the biggest stake and control everything, but instead having a popular cryptocurrency with APIs natively integrated with Facebook's services. It'll bring new users and developers to their platform, which has the real value.