Agreed. Federighi and his team are seasoned vets in building and delivering software to millions.

They aren't naive and know they need to balance end-user benefit with engineering's wishes for maintainability etc. Is the user going to see a vast difference in experience if they re-wrote the Settings.app? Swift is a language, not framework, so it doesn't offer the end-user anything worth caring about.

Swift will probably cost them more than it gains them in the immediate term, but the long-term is what Apple is all about, so I don't think they are concerned about this.

Obviously the sane approach is to write new code in Swift, including tooling and tests (as in Federighi's example). Not to rewrite and possibly breaks apps that are shipped to millions of users, just because of ideological reasons. Any software engineer who has worked on complex projects should understand this, no?