Bah! Cortana no-longer works!
I have been using Cortana over BT with my 1520 through 8.1 and early revs of 10...and she worked just fine. "Hey Cortana" would be followed by the sound from Cortana, then, a few seconds later, the ping from my headset (usually Plantronics Voyager Edge) that it was connected to my phone after which I could give Cortana a command.
That no longer happens.
Now, if my BT headset is on, "Hey Cortana" is followed by the sound from the phone followed by an interminable amount of time before my headset clicks on. Usually long enough for Cortana to decide that I just want to see the meetings remaining in my work day, the packages I am tracking and the latest news headlines.
Is the problem W10M? Is it the way it uses the BlueTooth Stack? Is it the 950 I replaced the 1520 with? Has she just gotten pissy? Who knows. Hopefully a fix comes soon.
BTW, notice that, on Fast Ring (Redstone Branch) Gadgets no-longer works either...