Another direction might be to extend Cordova to support macOS and Linux. Cordova already supports building UWP for Windows Desktop/Xbox/HoloLens using the native HTML+JS stack. Seems to me like a lot of existing Cordova plugins just need subtle nudges to support macOS in addition to iOS. Then you just need a good Linux solution and you cover all the desktop environments.

Then narrow the few missing desktop-focused APIs that Electron has but Cordova doesn't have good plugins for. (It would also be nice to support more Node-like background processes in Cordova and more Node-native libraries, but you would need to find a good balance that plays well with mobile.)