I think the attractiveness is that you can share Go code between applications on different platforms, which is not possible with Swift as long as the compiler and standard library is not open source (or generally available).

It may not always be better since you'll likely never be able to call from Go into Cocoa libs, but if you can write a shared library and use it on the server, iOS and Android, then it's a big win. Linking a Swift app against the shared Go library and calling directly from Swift into Go sounds pretty great to me.

I would never exchange the power of a ML based language with first class support from the OS vendor, by Go.