Facebook decided to re-license React under the MIT license after their original stance of not budging on the matter. This seems to come shortly after the WordPress team decided to drop React from the Gutenberg project, and was already looking for alternatives such as Vue.js and Preact. This re-licensing also applies to Jest, Flow, and Immutable.js.
This license will take effect with React 16, a release which is 1 year in the making, which promises to unlock some powerful features that will be very useful to developers. Regarding React and Gutenberg, this decision seems to be a bit late, as Automatic has already announced that they intend on dropping React from Gutenberg.
In his blog post, Adam Wolff addressed this change and wrote “In the wake of uncertainty about our license, we know that many teams went through the process of selecting an alternative library to React. We’re sorry for the churn. We don’t expect to win these teams back by making this change, but we do want to leave the door open.”