Earlier quoted context omitted.
Office uses react already: https://github.com/OfficeDev/office-ui-fabric-react
That’s not “Office uses React”, it’s a “collection of robust components designed to make it quick and simple for you to create web experiences using the Office Design Language.” Do you really see no difference between the two?
The React components are being used on production Office websites/webapps.
Source: I'm a Microsoft employee working on this project.