Interesting premise here
Personally, I think a "Mustang" created today from a Fiesta or Focus would likely meet the same fate as so many other similar cars. It would sell pretty well for a few years before heading into a steady decline as customers moved on to the next bright shiny object. By the end of the second generation it would be gone. ?
When Ford debuted the Mustang back in ’64, the car was little more than a rebodied economy car with a ton of trim and performance options. Given that same formula, what would the Mustang look like if it was designed today?