I've created a super-basic Xposed module that attempts to route your waze audio notifications through a bluetooth headset. The main goal of the mod is to interrupt your car's audio (regardless of what you're listening to - radio, etc) whenever Waze has something to say.
This is SUPER EARLY. I've only tested it against an Audi RNS-E bluetooth car stereo, and a google glass... I'll probably break if you get a phone call and are using waze.
Would love to get feedback on whether you use this, and if it works (or if it doesn't).
Source code is available on github : user: harrylepotter