[jacobolus]

For existing large applications (in particular, Adobe’s and Microsoft’s) OS X’s relatively quick change has been somewhat frustrating, and for any application there’s no need to replacing working code with newer different code just for the sake of it... but for new projects, OS X’s API “churn” has been great news, letting smaller teams tackle harder projects and create richer user interactions in less time.

I think it’s pretty reasonable to argue in favor of using new language features and APIs for new projects, assuming enough of the target audience is using platforms which support them.