Conversion to Swift is not something that must be done 100% at once (due to reuse of the Objective-C back-end), nor is it wise to change quickly (due to source

Conversion to Swift is not something that must be done 100% at once (due to reuse of the Objective-C back-end), nor is it wise to change quickly (due to source and binary incompatibilities that have been very clearly documented for the first few Swift versions). Slow-moving engineering teams, even within Apple, are just being wise; they can still be firmly behind the move to Swift.