The 2013 Mustang is due to get a small yet fresh redesign, taking cues from the Shelby GT500. Just as the 2010's got some influence from the '09 Shelby, it will address some things about the current models that people have been bitching/whining about (aka the rear end).
The rear end will be a bit flatter, and it will have a painted rear diffuser, GT500-esque front end, small interior design.
Powertrain: Around 425hp (up from 412hp), and for the V6: rumor's are circulating for the 250hp EcoBoost I-4 engine for the SVO model, and the 365hp EcoBoost engine found in the Taurus SHO for the V6 model.
And around 600hp for the GT500.
Right before the 2014/2015 Mustang is introduced as a "One World" model.