Go doesn't have method overloading, and it doesn't have polymorphism in the traditional sense either. (Not sure what effect Go's Interface inference has on H-M.)
I think it's ok. I would think it's like type classes, which work pretty well for Haskell. And Go doesn't need full-fledged type inference. I bet they could work something out that's simpler and more explicit.
Regardless, even explicit type variables would be very useful.
