It's not even clear how to fully implement things like class-side inheritance in a transpiler. The CoffeeScript implementation uses a definition-time copy of pr

It's not even clear how to fully implement things like class-side inheritance in a transpiler. The CoffeeScript implementation uses a definition-time copy of properties, which is probably good enough for many cases, but not all. That said, many of the features are sugar around existing patterns, like rest and default parameters to functions or arrow functions, so I expect that even an incomplete transpiler would be broadly useful as the specification solidifies.