I recently started implementing some interfaces for my structures and I was surprised to find that the default JSON encoder appears to try encoding the interfaces as if they were variables in structures. So for example if we have:

type Foo interface{
FooMe()
}

type Bar struct {
Foo
ImportantVariable string
}

The encoded JSON would look like:
{"Foo":null,"ImportantVariable":""}

Which is kind of silly, since Foo will never be anything other than null.

I think it would be useful for JSON to check if an imported variable is only an interface, not a struct or any other data structure, and ignore it completely if it is.