Earlier quoted context omitted.
Facebook has reserved its rights with their license and they can decide to enforce it at any time. Personal projects should be ok, but commercial projects should involve a discussion with legal. If the company thinks it's possible that they end up in a lawsuit with FB, it won't be allowed. For those who get caught unawares, they will have to move off react if possible, or seriously consider settling.
For personal projects, my interest here is in whether or not the patents license is compatible with other free software licenses (say GPLV3). That might be a consideration for some people.
(But don't ask me which licenses, I have no idea)