I’ve used it when toying around with some arm embedded stuff to have one module targeting thumb mode, another for arm mode, and then importing one from the other. I was actually surprised how well it worked.
It’d be nice if struct layout could be guaranteed to be identical in cases like that, so that you don’t need to use extern everywhere and can avoid duplicating std code. But I doubt it’s likely to happen, as I could imagine it being a pain to implement properly and has less use cases nowadays.