This is truly awesome. I don't understand some of the negative comments above.
- There are advantages to static typing (and in modern day static typing you tend to type less). Some of the extra complexities you take out from static typing in making a dynamic languages could simply reemerge in other places in your development process.
- There is virtually no learning curve for the superset if you know JS and some basic OO. Being a framework there is always the risk that if you take a dependency the framework could go out of date someday - this is a more universal problem. The open source nature of the project could probably help here.
- As already mentioned the advantage of TS compared to Script# is that it interoperates better with existing or new JS libraries. Providing wrappers could quickly go out of sync as the libararies evolve.