Chiming...
I don't have much to offer regarding the 'new' FS class and the relative performance potential of the current and forthcoming players, although the 2015 Mustang looks like it will be raising the bar for the American muscle, again. I wouldn't be surprised, however, if it ends up in another class.
Last year, we were pretty optimistic about our chances going into Nationals and felt like the results were 'per plan.' I let a class win slip away, but the car is very good. Another year of tuning and the legislated reduction in grip will make the M3 a force, IMO.
(JP, my Nationals "report" is here:
http://www.m3post.com/forums/showthread.php?t=885123 )
Here is video of my daughter's final run, East course:
My final run, East course also: