According to Mustang Source, the all new 2015 Mustang GT, available in spring 2014, will have a choice of Ecoboost v6 or 5.0 v8. The power could be comparable but my choice would be the 5.0 (unless gas is $10 a gallon).
I'd be all over this like an addict in a poppy field if it were actually cheaper then a GT V8. But considering its got the Shelby name stamped on the interior, me thinks its going to cost significantly more. Equal money, and I go for the V8 every time. Make this substantially cheaper, and its suddenly more interesting.