Not all software that includes react is SaaS… like WordPress, my software would have included react-based Ui components in a future version. It’s “shipped” software that someone downloads and installs. I am concerned that I’m limiting my audience by bundling with this kind of licensing – even if *I* don’t have patents and worries about protecting them, some of my users are at large corporations who definitely would!
And the current scope of facebook’s activities isn’t a good indication of where there might be patent conflict, either. They are working in the self-driving car space, amongst others, for example. 15 years ago, no-one would have expected that search engine company to be one of the top mobile phone OS makers, or an online bookstore to be defining new models of computer consumption.