So basically if you have this awesome, let's say, middle out compression algorithm patent, and have an interface in react, then they can use your middle out without being sued? (Just trying to clarify what you are saying here..)
Your license to any patents which Faceboook may or may not have that cover elements of React will terminate. At that point, Facebook may choose to initiate a lawsuit against you over your infringement of whatever React patents (if any) they have.
So if you have (or are planning on obtaining) software patents, the React patent grant may not be very valuable. (Then again, Facebook may not have any patents actually covered by the grant, in which case it's not valuable to anyone.)
(1) Have patents / use a react alternative, such as vue (note this is annoying since there is no cross-platform native app version of vue ) (2) Don't have patents / protect your intellectual property in other ways (maybe by publishing a public whitepaper or something) / use React / Bust your ass since facebook can likely implement better and faster than any small team.
It's important to keep in mind that there are two different types of Intellectual Property in view here. Software licenses and patent licenses. Theoretically, you could use some software Y under the BSD license and have some third party X sue you because Y violates a patent (even though you didn't write Y and are only using it). Facebook is being generous IMO by saying both A) you can use our software and B) if we have patents that the software benefits from we also license those to you provided C) you do not sue us for patent violations, in which case we revoke B (but not A).
So, going back to the article, the license to use React would not be revoked and it has nothing to do with competing with React. It is possible that if you sued Facebook for patent infringement AND Facebook claimed that React benefited from it's patents, that Facebook could now sue you for patent infringement b/c you use React.
But, if you sue any big company for patent infringement, they are also going to look at their portfolio of patents to see what you might be infringing and will counter-sue. So, in that case, I don't feel like Facebook is really being contrary here. They are basically saying, "As long as you don't sue us for patent infringement, we promise not to sue you for any patent infringement related to our open source software (including React). By doing this, we are hoping you will take advantage of the software we have put out there in the OSS world and alleviate any patent fears you might have. However, if you choose to sue us for patent infringement, we revoke this promise, and are going to treat you just like any other Joe Schmo."
IMO, Facebook is going out of their way to make it possible for others to benefit from their OSS software by granting not only a generous software license but a related patent license as well. For the article to misconstrue this as a license revocation if you decide to "compete" with them is pretty disingenuous.