I've often thought about a CoffeeScript variant with optional typing that transpiled to TS. The types would be ascribed via a backslash, e.g. `(hello\string) -> hello + ' world'`. But considering the huge benefit of TS is the tooling such as intellisence, I doubt it's worth the effort to start a whole separate ecosystem.
I envisioned it somewhat the opposite way. Gradual types a-la TS tacked onto CoffeeScript. No actual TS integration per-se.
Though even better would be if the TS team could figure out a way to factor out the type inference logic so that it could be applied just as simply to CoffeeScript as to Javascript, and even allow definitelytyped defs and perhaps intellisense logic to be reused everywhere.
Roslyn does this somewhat for C# and VB, so it might not be too big of a jump.
