I assume it will be fine as the iPhone 5S, 6 and 6+ allow 2 simultaneous bluetooth connections at any given point ( ... the older devices seem to allow 3 for some reason... the change seems to have been when they introduced 64bit devices as it is the same for iPads)
At the moment I have my iPhone 6 connected to my VW via BT and a "Mobile Home" button to allow me to access Siri.
the interesting port will be the audio routing and if multiple options exist you can select which one you want to use... so I assume it will allow you to route calls via the car bluetooth ... or the watch.
Guess we won't know for sure until we get our hands on the Watch and test it with our cars... because also I have had weird things happen with different headunits such as Alpine where it would not connect to the headunit every time for some reason
THIS. I've been really wondering how the watch will fit in/interact in my car. Car is connected to phone via bluetooth. Right now, even if I press and hold the home button Siri pops up but takes ~10 seconds to route the audio over the speakers and THEN I can finally talk. So my questions are: If I use Siri on my wrist, will it stop music playing on my phone? Also, will the watch try to route Siri over the speakers just like my phone? If I get a call in the car, where is it routed (car or watch)?
I guess there's no way to really find out but to wait and try it out... I'm hoping it doesn't pause music, and it doesn't try to route Siri over the speakers (don't like the weird ~10 seconds of limbo where I don't know whether I can start talking to Siri or not...)
I do have a feeling (and really hope) that where the phone call is routed is dependent on where you press the answer button. I hope it's smart enough that if I answer via the button on the steering wheel it goes over my car, and if I choose to answer it from the watch it routes through the watch.