I'll believe it when I see it. I still believe he's winning the Rumble again and winning the World title at Mania.
If this heel turn happens, I half-agree. Reigns and Ambrose will win the rumble in a controversial finish. If the heel turn happens at NOC or HIAC, then for the 2-3 months previous, they'll trade wins on PPV, then have the face-off as the final two in the rumble, they'll both win, and it will be a shield triple threat at WM32.
Whether Reigns or Ambrose wins, I guess depends on if it's the main event. I doubt WWE would send the fans home with a heel win, so Ambrose would win. But if a bigger match like HHH/Rock or Brock/Rock main evented and shield triple threat was the 2nd to last match then I could see Reigns winning the belt.