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Swift is easier, faster and safer than Objective-C and therefore better suited to app development.
In 2 years, popularity of iOS programming languages dropped by 67%, from 3rd to 14th place on the TIOBE Index.
Apple shows no interest to re-write their own code in Swift. As long as the system core itself is written in ObjC, it won't become obsolete.
Apple did move their core libraries over to Swift.
it ain't gonna happen any time soon. There is a tremendous legacy of frameworks and libraries that are difficult or impossible to access without an Objective-C shim. (See the HIDManager for an example)
If you build an easiest way to write a code that end in the same result, it'll be prefered over time.
Apple is devoting a tremendous amount of time and energy to the development of Swift and the language has seen an unprecedented adoption rate in the last year.