Swift's high-level syntax will probably open up iOS development to many people who otherwise would have seen Objective-C's square brackets and run away.
I like Go a lot, but Google switching to it for Android would probably have the opposite effect. Many people learn Java in school. Almost no one learns Go.
People don't learn Objective-C in school, but it has not slowed down adoption of the language for the iOS platform. If the platform is popular, and a language supports it well, programmers will learn.
I like Go a lot, but Google switching to it for Android would probably have the opposite effect. Many people learn Java in school. Almost no one learns Go.