They already said there won't be 2 shelby models produced at the same time, my guess is the will run with the gt350 for 2-3 maybe 4 years then make a mach1 with pretty much all gt350 underpinnings and then they well make the new hellcat munching gt500 somewhere around 2018-19
UPDATE (3/8/16)
Standard Equipment, Going Fast: Shelby GT350 Mustang Owners Get Complimentary Performance Driving School
GT350 Track Attack program gives owners of new Ford Shelby GT350® Mustang hands-on track instruction with Ford Performance Racing School...
I know there are many who wish to keep their halo mustang as stock as the day she rolled off the line, but then there's people like me:D who already have a pre-thought out modding plan for the car way before I even buy into it, I don't do cause I'm unhappy with the stock setup but because I know...