I wonder how Matt reconciles his absolutist stand on the GPL ( see Thesis and that vendors selling non-GPL licensed software can't sponsor WordCamps, etc) with using a clearly encumbered package like React.

It was one thing to consider it when it was possible that FB would loosen the license and making it BSD vs GPL strikes me as a minor issue. But leaving it as is and using it in WP also strikes me as a close to hypocritical stance for someone who's so vocal about the rest of the code, even plugins and themes, being GPL.

WordPress’ new Gutenberg editor is also built using React, as the project’s chief contributors are employed by Automattic

The entanglement between Automattic and WP has always been problematic. In general, it's been far more to the good side - I think that's obvious. But when there are major, directional decisions being made I don't know a) that any one contributor should have such overwhelming weight in making the decision and b) how the interests of each party are reconciled. WP the project shouldn't be saddled with React officially just because a relative handful of developers at Automattic like it.