So apparently this is the rear end captured from a YouTube video that got pulled.
Honestly, I think this rear end is no better than the 2010 - 2012 rear end that not many cared for. The 2013 and 2014 Mustang rear end looks pretty sweet.
I'm sure the GT version, which will likely have a rear wing, hood vents, different grille and maybe wider tires will look better, but not sure that's going to make me care for it much more.