I don't know if it's the iOS 8.0 release. I'm a developer and used all of the beta releases, then the gold master release and had no problems. That's right - zip, nada, NO issues with any Bluetooth connectivity on my iPhone 5.
Initially with my iPhone 6 Plus, which I did restore with a backup of my iPhone, I had not problems, but after installing the iOS 8.0.2 update, I can no longer place a phone call from my 2014 Mercedes ML350.
I can do everything else with my iPhone and my car except place a phone call. I can stream Bluetooth audio from my iPhone, but when I switch the infotainment system to the phone section, I get a big notification of no connection with my carrier, even though on my iPhone I have anywhere from 2 to 5 dots. I can place a call from the phone if I were to pick it up and hold it up to my ear. The problem is that using a cell phone in my car in that manner is against both state law and on-base regulations (I work on an Army base). Furthermore, if I have a hands-free system in my car, I want to use it as such.
I'm trying out the first iOS 8.1 beta and will post my results later today.