I simply do not see why your goals 1-4 require a) the same language on the server as the client and b) the use of a non-blocking I/O model at the server. It appears to be a leap of faith on your part.

While marshalling of model objects to JSON is obviously going to be easier to achieve if your model objects are Javascript objects, marshalling to JSON is trivially achieveable in almost all programming languages.

To suggest that developers should - to achieve this microscopic payoff - choose to build servers using a language with a crippled concurrency model (i.e none) is laughable.