We worked in the context of ES4 on gradual typing -- not just inference (as you imply, H-M is fragile) -- to cope with the dynamic code loading inherent in the client side of the Web. Gradual typing is a research program, nowhere near ready for prime time.
Unsound systems such as TypeScript and Dart are good for warnings but nothing is guaranteed at runtime.
A more modular approach such as Typed Racket could work, but again: Research, and TR requires modules and contracts of a Scheme-ish kind. JS is just getting modules in ES6.
Anyway, your point of reference was more practical systems such as Java and .NET but these do require too much annotation, even with 'var' in C#. Or so JS developers tell me.