This would be easy to add. In fact, the implementation includes an @_opaqueReturnTypeOf attribute for compiler-internal use by printed interfaces, since it's necessary in order to represent associated types that were inferred to opaque return types (although it uses mangled names for full specficity so isn't ergonomic for end user use at all). From what I've seen of Rust adoption of impl T in Rust code and from asking Rust community members, it doesn't seem like a huge problem not to be able to refer to the type names in practice.
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