(I'd love to see native Android apps in Python (or Nim) but that's probably never going to happen. Failing that I could live with a language like Swift.)
Swift has a lot of developer growth, cross-platform library possibilities, and a two optimization pass compiler (SIL and IL).
Also, I wouldn't say the rust language definition is less stable than Swift's, which is still very much in flux (with changes such as the removal of C-style for loops in the pipeline or just released)
Also, Swift doesn't do garbage collection. That may cause problems when trying to build a shared GUI famework.