> This allows Apple to switch to intel chip on iPhone, or switch to an ARM chip on MacOS.

I think you're assuming way too much. Says Chris Lattner regarding Bitcode, "It's useful for very specific, low-level kinds of enhancements, but it isn't a panacea that makes everything magically portable." [1]

[1]: http://atp.fm/205-chris-lattner-interview-transcript/#bitcod...