Why I don't think it will matter
Most of what they have done in TypeScript has been done before. It looks exactly like ES4 from the code snippet shown, and that was a huge failure. The writers sacrificed the strong points of JS in an effort to bring bad parts of other languages into JS. The only real implementation was ActionScript3. To me it looks like MS just said "Hey, lets take ES4 syntax and compile it to ES5". Not exactly ground-breaking in my view.
I used to be a lover of strongly-typed languages and had a hard time when I started with JS. But over time I came to realize that forcing typing most of the time was just not all that helpful (it helps the compiler, not the developer). Interfaces are only needed it you have strong-typing. Generics are only needed if you have strong typing. Take away forced types and they are no longer needed.
To me, this is another example of trying to fix something that isn't broken, and force Javascript to behave like a preferred language. The driver for this language is the fact that Visual Studio sucks at JS, so they needed a way to change the language to suit their product. If you want to write in a language like C#, write in C#.
Also, why say 'promises to offer JavaScript developers new features, such as proper classes' - is this implying that JS does it improperly? Javascript doesn't have classes by design. And personally, I find it much more expressive and easier to work with because of it.
Does Javascript have problems? Yes, it does. Is it fundamentally flawed? No. If it were, it wouldn't be so popular. The biggest reason for the recent outcropping of cross-compilers is the fact that developers are lazy and just want JS to work like [insert favorite language here], instead of learning the language.
