I see that you're targeting website creation, but a react-native syntax output (https://facebook.github.io/react-native/docs/flexbox.html) would be nice for me. It's just slightly different (it seems, to me) than vanilla flexbox.
Interesting use case I hadn't thought of. I'm making it in React and then converting it all to standard HTML and CSS so it would be simple to do a standard `react` output instead.