You are approaching the issue but from the other direction :) It is indeed subtle. It could be solvable though if someone wanted to change the current behavior, in a forward compatible way.

Hint: "Don't use pointers at all" is the requirement that you would have to relax. That means that you cannot know whether a pointer is safe or not to be used from within an interface.

Conservatively, that means that every nil pointer in interfaces are unsafe.

Which means we should either have a way to check for nil pointers (typed or untyped) in interfaces or assert that an interface value cannot contain a nil pointer. (requires definite assignment analysis)

Actually have implemented the nil checking migration part as a POC but seems that it requires the assertion part to be tractable... That is a bit more work.