Google has enough resources for someone to write a transpiler that can take annotated JS and convert most of it to TypeScript. It's certainly much more pleasant than having to type random comments everywhere, which kinda makes syntax highlighting way less useful. Oh, and last I checked there were no editor plugins for linting Closure Compiler annotated code.
Another option would be to add TypeScript support to Closure Compiler, although it doesn't seem likely since there's no spec to guarantee compatibility.
I'd love to see Facebook, Google, and Microsoft team up in this space, instead of creating 3 separate but very highly similar tools.
Also, while we're talking about Closure, let's take a moment to appreciate its amazing UI toolkit [0]. I'd still consider many of their widgets to be the gold standard. It's written with desktop clients in mind and is incredibly feature-complete. I believe it also has pretty good accessibility, although I haven't personally tried that out. Oh, and don't forget the i18n as well! The closure library definitely has a lot of quirky aspects to it, but it's still quite amazing if you consider its age and how much stuff it supports. It's worth taking a few minutes to browse through their docs [1].
[0] https://google.github.io/closure-library/source/closure/goog...
http://www.syntaxsuccess.com/viewarticle/closure-compiler-vs... - interesting article about how closure enables smaller bundle sizes.
I agree, it would be cool for someone to do the same thing for Typescript, I seem to remember a repo a while back on Github that said someone was experimenting with it - cant for the life of me remember where though!