you know, think it may have been GM that invented the idea of a new style car for each model year. As that became expensive, it evolved into a new style car for every 4-6 years. I am not sure it is all that necessary. GM only did it so people would buy new cars.
Think of how many times a total body restyle has ruined a car. I think subtle changes from year to year would be better. Look at the porsche 911. Same body style since 1963.
You start with something that works. Which, ideally would have been the 65 mustang, but since that is long gone, we can start with the S197. Then make small improvements as necessary. Because Ford stuck with the S197, they were able to offer a good interior (for once) in the 2010s. Next will come an even better engine, then an even better suspension, etc. etc. and by 2020 you'll have a real ferrari killer. (okay, maybe just a porsche killer)
Instead, Ford will redesign the S197 in 2014, to something new and odd. And we will all hate it for a time, and it will have bugs, and they wont be worked out until 2019.