Unioning interfaces like this does seem convenient for composition/mixin patterns, I'm not sure if extending it to structs in general seems worth the cost of potential footguns though, especially external libraries and such where you probably don't want to think about the full potential tree of embedding conflicts.

I’m sympathetic to parts of the Go design philosophy, but the only thing that comes to mind looking at this is “damn, that’s some awkward (nominal-looking) syntax for (structural) intersection types”.

(It also feels to me that this sort of anonymous embedding is materially different for interfaces vs structs, though I admit that from a type-theoretic perspective it’s not.)