Swift is changing fast. Chris Lattner has stated that Apple will have a good migration solution to update current Swift code. If Apple does it right, Swift will be a major cross platform language within a few years.
You can argue that Rust, Nim, or Go are better, for example, but the community and support Apple give Swift give it a big advantage.
Simply look at the number of Swift books published in the first 18 months:
If anything, I'd argue that we're in the middle of a fantastic time for languages. I have at my disposal Go, Rust, Swift, and Nim, not to mention a re-emergence of Erlang (and birth of Elixir), Clojure on the JVM (and what the heck, Java)...
There's so much happening in languages now, it's a wonderful time to be a developer! People will always argue about which is the best, why Go needs generics, etc., but when you're a "right tool for the job" kind of developer, your toolbox is looking pretty sweet right about now.
You can argue that Rust, Nim, or Go are better, for example, but the community and support Apple give Swift give it a big advantage. Simply look at the number of Swift books published in the first 18 months:
http://www.h4labs.com/dev/ios/books