I think this would be possible. The GC and memory management between nim, c, and switch would be a constant pain point. You would have to export c style structures. It might even make sense to write the header file in C as glue and have both nim and swift use it.
One use-case I can see is some thing like a network/database support lib that can run on all platforms while UI is drawing natively with Swift on iOS or Java on Android. I would rather just write whole apps in nim though :)
