> Lack of polymorphism also means you don't have to guess about concrete types when reading code. When troubleshooting, you can see what's going on without going through whole inheritance tree.

Parametric polymorphism would mean you never have to even consider the type of the code. It's a freeing abstraction with plenty of very simple reference implementations. And it lends itself to composition over inheritance.

And sadly I doubt Go will ever manage to get it.