Well, I don't know the answer, obviously, but I wouldn't quit my day job.
As someone who needs to write an iOS app, I'm going to use Swift, and the tooling built around it. Transpilation would mean you either need to integrate a debugger (hard) or I'll have to debug transpiled code (and have to check the transpilation)--I have enough "fun" doing that with ES6 in the browser. No thanks; I'll stick with the supported tools.
As someone who needs to write an iOS app, I'm going to use Swift, and the tooling built around it. Transpilation would mean you either need to integrate a debugger (hard) or I'll have to debug transpiled code (and have to check the transpilation)--I have enough "fun" doing that with ES6 in the browser. No thanks; I'll stick with the supported tools.