We had an app early in dev, and decided to make the leap from ObjC to Swift. Swift is here to stay, and as with most things the longer you put it off, the harder it'll be later. The integration between Swift & ObjC is good, so existing projects can be converted slowly.

Avoiding the conversion because Swift "isn't ready for primetime" or "the debugger is buggy" seem like excuses people make for "I don't want to expend the effort to change".