While that did look cool, I think youre forgetting that youd have to fight as well. Thats where this idea would fall apart. The combat probably wouldnt be so great.
Make it for Kinect so I can learn to jump out the window and kill myself before I realize how shitty the game is....
In all seriousness... I don't see this idea working out very well. The benefit of playing open world games in third person is that devs can forgo many of the smaller details that you would otherwise notice in a first person game. Something like this would be a huge undertaking.