I'm currently developing with Expo with plans to expand to Electron (though I haven't written anything for Electron yet, just the React-Native and Expo portion) but my theory is that once you have the core React functionality down (The API endpoints, Reducers and Actions (if using redux), and general component structure) then porting to Electron will be fairly trivial.

React-Native has a lot of cross-over with React for the web. So I'm hoping when the time comes my port will go smoothly.