Could facebook change the license at any time for future versions? I guess at least they couldn't do that retroactively for previous versions since those are already "released".
Of course. As with any project, with the agreement of all copyright holders, you can relicense at any time. Facebook has already changed the license twice.
You could, if you wanted, fork the original Apache v2 licensed version that didn't contain the PATENTS file. (Although as per the linked article, why would you want to?)
You could, if you wanted, fork the original Apache v2 licensed version that didn't contain the PATENTS file. (Although as per the linked article, why would you want to?)