There has been active public development on ReactXP [1] for months now. It supposedly works with React-Native and React-Native-[Windows|macos].

Considering the amount of work being done in public on React-Native-Windows [2], it looks like this is turning into one of their (intended or not) version of cross-platform (using web technologies) dev stack.

[1] https://github.com/Microsoft/reactxp [2] https://github.com/Microsoft/react-native-windows