No, people have been against breaking compatibility with old source, like changing how certain statements are parsed and executed that would have made old code

No, people have been against breaking compatibility with old source, like changing how certain statements are parsed and executed that would have made old code now in error. This is why strict mode is opt-in and larger ES4-like changes are dead in the water without careful design. On the other side of things, though, new features that break in old browsers are added all the time. Try and run Date.now or Function.bind in old browsers and they'll immediately throw an error. It's only through polyfilling (and in some cases transpiling) that sites work in even IE8 today, and it will be the same situation in the future if a site wants to still work on an old Android or iOS device. But yes, staying up to date as a user does depend on a newish browser being available for the platform you're running, and it would be great if old devices could continue to get updates. Really old iOS is out of luck, but Firefox supports back to Android 2.3, so users stuck there can download that browser to continue browsing the web.