But as author is also talking about the environment and I know it will improve but if you in to this and you have large codebase than waiting 10 minutes (some times it take 20 minutes thanks to Xcode 8.2) for build compilation and with every new Xcode release and swift release things are getting change so fast that most of time it is very hard for production app quality. Also not all dependencies keeping up at that rate.
That said I really love the language but it's my opinion by looking other languages swift is not for server development and will not be successful. But that's my opinion.