And it's only for nightly (see "feature") and it means it's can be used in reliable code. Talks about stabilizing of this feature are endless.
The idea would be that these types would be put into a library (or just another module) that's used by the rest of the app. There wouldn't be duplication of these structures. It's not ideal, which is why we are working on stabilizing the compiler features to do away from codegen.