[ballenf]

They would simply sue a particular company for employing infringing technology. They wouldn't have to nor want to make any broader claim than necessary to achieve their goals in the case at hand.

It would likely be a company suing FB for infringing a patent who happens to also use Preact in a site. FB presumably wouldn't have access to the site source code (pre-suit), but would be looking at the compiled, minified public site. I don't know how Preact and React look when compiled compared to each other, but given their similar structures it might be hard to tell them apart. FB would identify the offending bits of code or code structure. They wouldn't need to even use the word "Preact" (or "React") in the suit.

If the underlying suit was a patent troll suing FB, FB's use of React patent clause might actually be celebrated in a enemy-of-my-enemy kind of way by the broader developer community.

It would require FB to finally disclose the patent numbers applicable to React. I've spent a few hours attempted to review FB's patents to find anything related to React technology, but it's a needle in a haystack challenge and I failed. There are tens of thousands of patents and impossible to know what keywords to search for. (If someone else has done this work, would be great!)