Apple needs to do this for Swift and native development to stand a chance out there. Releasing Swift just fragmented the hell out of Apple development for years to come. No Apple developer can afford to be not be an expert in both languages now. But the new language and it's unstable state means even greater chances of projects going non-native IMO. So Apple has got to get Swift into a stable state and they have to do it fast. How many more things are going to change and break existing code before the dust settles? This thing has been years in the making and still no sign of stability. Swift is cool, but these are very early days still.
I wholeheartedly disagree with this. If there's any indication from the developer community, it's that they have praised Apple's last two major updates to Swift. It may still be evolving, which was said from the moment of it's induction, but it's not unstable by any means.
You speak of stability directly as stagnation of foundational development but since the update cycles are slow and consistent, and expected and welcome, you've got to weigh the pros/cons appriopately. It would be completely irresponsible to simply dump a language like Swift into developers laps and simply never adapt to the needs of those developers using it -
that would cause projects to go non-native as we can see with the trend of Objective-C switching Swift. Swift has a roadmap, but it's heavily shaped by the people using it. Plus, we're talking about iOS developers, who are already familiar with this type of update cycle.
I also think that you hardly need to be an expert in both languages, nor that achieving an equal level of familiarity across both is an impossibility or even that complex. The languages relate to each other and based on the resources available, many new-coming iOS developers who orient themselves towards Swift will pick up syntax on Objective-C, because they'll see it in parallel.
If someone feels Swift is too immature to even warrant attention, then that's the developers propagative. However, trends among mainstream iOS developers don't give a damn about any single one's hold ups. Development in Swift will be pretty swift because regardless of what people feel, it
is a good language that has adopted really good features from other modern languages
and it is going to get better.