Late last night I made a breakthrough and finally got the Go Objective-C bridge working. This just shows a "Hello world" window so it might seem like that's all there is. But the hard work has been in making the bridge code work at all for any kind of method call.
What this means is any Apple API can be used from Go. And since Apple has schemas for every one of their APIs, I can generate wrappers for them so it all feels like native Go.