Our north star is to serve the people who want to make awesome stuff for phones and the people who use that stuff. We've been working with React Native since that technology has done the most to push mobile development forward in a significant way but we're always looking around at other things like NativeScript, Flutter, Kotlin, etc., etc.
We don't consider Expo to be a React Native company -- instead, we think of ourselves as a mobile development ecosystem. So, we might end up working on any of those things, though we don't have any concrete plans right now.