The more likely conclusion is Microsoft is open-sourcing a tool the found useful internally when building large JavaScript apps.
Suit: People aren't using Visual Studio for JavaScript, why not?
VS PM: We can't do Intellisense properly, so people are using Sublime.
Suit: What can we do about that?
Anders: Let's create our own language that works better with VS.
The more likely conclusion is Microsoft is open-sourcing a tool the found useful internally when building large JavaScript apps.