The transpile issue on mobile is greatly overstated. The vast majority of mobile browsers (by market share) have very good es6 support. Instead of one version,

The transpile issue on mobile is greatly overstated. The vast majority of mobile browsers (by market share) have very good es6 support. Instead of one version, websites need one with minimal transpiling and one with full translation for older browsers. Sure you need a little more setup, but it's not only better for clients, but it's also much better for development because your source maps, breakpoints, and actual variables are much closer to what the browser is actually executing (this is especially important for generators because they compile to case statements that aren't easy to debug).