Interesting, if not unsurprising analysis of the top 100 free apps in the iOS App Store. Apparently only 11% of them include any Swift code:
I once again downloaded the top 100 free apps and wrote some scripts to analyze the .ipa files. It surprised me to find that the vast majority of the apps in the top 100 are still building without any Swift.
Most of the top apps in the App Store have been the top apps in the App Store for a long time now, and there's very little incentive for them to start developing with a new language. Not to mention the large amount of games in the top 100 that are likely written in a game development framework like Cocos2d instead of in straight Objective-C.
I'm of the opinion that it's kinda silly to start a new project in anything other than Swift, and I'd be willing to bet that most iOS developers would agree with me.