On TypeScript, are you seriously asking for warning-annotations? The class syntax is in for ES6, not original to TS. Or do you mean 'interface' as structural type (record width subtyping relation) declaration form?
I haven't had time to use TS much yet but the combination of structural type system (not needing to inherit from IFoo, if you have the members it's enough) and optional typing look like exactly what I want.
Hopefully this pays off in terms of not only self-descriptive code but also greater support for refactoring tools.
In many ways, TypeScript is the "anti-Dash" (see leaked Dart memo). It builds on ES6. It does not inject novel runtime semantics. It just checks annotations _a la_ JSLint. Smart!
