Today in my car (2010 Prius) I noticed the Bluetooth interaction between the car and my iPhone 6 is MUCH smoother. Ever since I can remember (iOS7?) it used to go into a calling screen on my cars dash screen. It would work okay it was just slow and clunky. Today when I used Siri it responded quickly and I didn't get the old calling screen. I went straight from iOS 9.0b5 to 9.1b1 (didn't load the GM). I don't know if this is in the release of iOS 9 or only in 9.1.
That would be nice. The calling screen was a bit clunky like you said. But I also use it as a point of reference to know that Siri is activated (that and the beep that comes through the speakers)