Interestingly, it's possible that Microsoft will soon have the best concrete numbers here; as it moves more and more towards open-sourcing key components of their developer tooling, it will be able to compare everything from talent pipelines to internal developer productivity before and after the sea change.
That said, could Facebook capture more of the "React consulting and services" market? Could it, for instance, offer hosting for component sandboxes, or develop paid tooling that builds on React for rapid line-of-business application development? Possibly, but it would be such a drop in the bucket compared to any other use of a Facebook engineer, that it's not worthwhile. There's value to shareholders in a company, however large, having a "cohesive focus" in its lines of business.