Well I can tell you how a simple Peugeot 208 manages to handle all that perfectly easily - don't make escuses for Tesla. Elon doesn't want to do it because he doesn't like Apple. He said he had his own mirroring option and like most of the crap he comes out with, it never materialised either.
The floating window would work just like any part of the music system currently does, just swipe it down when you don't want it - it never covers up the AC controls. You can still adjust the volume on the Sat Nav in the 208 as well, no problems. It's not something you'd ever need to change more than once, hell I don't think i've had a sat nav voice "on" for about 10 years now either, they drive you mad.
I really wish I could turn the voice button my steering wheel into a Siri button, the built in voice commands literally don't work on my Model S, it never heard me, absolutely useless.