That’s a really good question.
I don’t know the answer, but I can only add, that this statement has been present in the docs for at least several React versions (or maybe even from the very beginning of React? I don’t actually remember the times when it wasn’t there).
One more thing is that many popular libraries depend on context, and that would be probably all the libraries that feature some kind of
provider component, that should wrap your app: react-router, react-redux, mobX, react-apollo (because it’s based on redux), etc. Basing on that, I dare say, that Facebook won’t remove the context functionality without due preparation of the society.