To me, "JavaScript and Dart" would also be a depressing future. You may hate JavaScript and like Dart, but there are a lot of people who hate both of them and

To me, "JavaScript and Dart" would also be a depressing future. You may hate JavaScript and like Dart, but there are a lot of people who hate both of them and would prefer CoffeeScript or Elm or purescript or JS+macros (sweet.js) or C# or C++ or ... IMO it is much better to focus on improving compile-to-web support with things like bytecode, better debugging, threading, custom value types, hooks into the garbage collector, etc., etc. - making it feel more like "compilation", less like "transpilation" (to the extent the term implies that you have to look at the output) - than to change the number of blessed languages from one to two. The result, if used to compile Dart (or any other language), might sacrifice a bit of performance compared to the maximum achievable by a dedicated Dart VM, but not that much, and there are myriad advantages.