That sounds like it's actually a complaint about strong typing -- if everything's the same type, you can do that now by passing around first class functions.
Aka polymorphic function parameters. If I manage to abstract a bit of functionality into a function, I don't care what the type is as long as the operations within the function work on it. Haskell uses typeclasses to provide this guarantee for specific types. Go seems to try to do something like this with interfaces, but it doesn't seem to apply to the map/fold/filter style of programming