It would not be a new logo, it would be an updated version of the same logo. Cadillac just dropped the wreath to stay modern. Starbucks zoomed in their logo and removed all the words. Microsoft simplified their logo recently as well.
A new Mustang logo would still be a galloping horse, it just might look slightly different. Maybe it would be fit into a circle, or maybe it would get simplified.
It's also possible they will never change the logo. After all, the Ford blue oval hasn't changed in the longest time.