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.

I love Go; having Go as an option for Android development would be awesome because the language is just so much fun. I'm not getting my hopes up though, because Go was intended for server-side stuff. Object-oriented design is a great strategy for rapid app development, and this is the key different between Swift and Go that I've noticed.