Apologies, polymorphism is a loaded term that could mean different things depending on your background. I mean parametric polymorphism, i.e. generics. What makes you unexcited about them?
I surely see the value, but I'm also convinced by the idea that they will complicate the language, and, in practice, after a year or so writing fairly serious Golang programs (I wrote the emulator and debugger backend for Microcorruption in Golang, for instance, along with a pretty complicated web fuzzer) I haven't missed them.
