you even write once, render anywhere
Smells like future front-end!
Note: if you write games - it's not your story, sorry
Is React mature enough for WEB? Yes, the most.
Is Electron mature enough for Desktop? If you like VSCode, Atom, Slack or some of 385 apps and believe in GitHub (Microsoft) - Yes.
Is React Native mature enough for Mobile? If you like Facebook, Instagram, Skype, Airbnb, Walmart and other apps and believe in Facebook - Yes.
To Be Continued…