No, interacting with UIKit is just one example usage, though important enough to warrant special constructs like that. The people that seem most excited to me are those that work with server side Swift.
But i don't know if it will be the most performant implementation as it will depends of how much state copy between threads its involved (as this is the common bottleneck in performance on a multi-threaded implementation).
So a more classic implementation might perform a little better, but i don't know if this will also stand true in Swift as the compiler might use tricks behind the curtains to optimize things giving the people behind this also control the Swift compiler.