I've worked on a million line Go code base and a dozen open source projects and many typical backend services, and interface{} is actually quite rare outside of something like json serialization or string printing - i.e. fmt.Printf(msg string, args ...interface{})

I almost never see code that application developers write using it, and usually if someone is writing that code, it's wrong, and I help them figure out how to avoid it.

Usually you can avoid it by using closures or interfaces.