Clojurescript a lot of its success to the use of the Google Closure compiler, which really shines when you transpile because you can ensure that the resulting js is suitable for the Closure compiler.
Yes. Angular is working on a similar approach. Great results so far.
I read there was a TypeScript Compiler that would output CC copatible type annotation comments.
Tsickle by Angular does that: https://github.com/angular/tsickle
It wraps the TypeScript Compiler and outputs CC compatible type annotation comments.