I went to check this out, seems they're only focusing on React and beyond that, a maintainer mentions they're looking for funding. Doesn't sound too promising...
A lot of this has morphed into the unfortunately named FAST framework, which focuses on web components rather than react. However, they have both Microsoft fluent and unstyled flavors, in case you just want to style things yourself and not look microsofty
https://github.com/OfficeDev/office-ui-fabric-core/issues/12...