A few places have linked to Apple’s use of Swift in iOS, it’s useful to put it in context.
How much of Solaris was made out of Java? Almost none. There was a web browser that you’ve never heard of called HotJava, and that shipped with Solaris, but that’s it. The rest of the OS remained resolutely C with Motif (later GTK+). While Sun wanted us to believe that Java was the developer toolkit of choice, they never chose it themselves.
A hammer is a mighty tool, but you cannot use it for everything.
The message behind Turing equivalence is that programming languages are functionally interchangeable. If the Swift evangelists at Apple can convince Apple people to use Swift, where the Java evangelists at Sun could not, we learn something of the difference between those two contexts.