I am also not sure why this discussion is here and what is it about.
Z06 in my opinion is much more interesting car to work on. Buying stock Mustang and making a track toy out of it is very possible but in my opinion any choice of Lotus Elise, S2000 or even Miata will deliver much more pure lightweight fun. Mustang does not fit into category of light fun cart style autocross cars.

And if you speak about muscle car - Mustang hardly fits into this category as well. It is where Z06 is king. I was thinking about getting such car more than once and modding it to the limit. May be one day if I get 3+ cars garage I will do it, just for fun.

Spending money and time on stock Mustang transforming it into track prepped car does not imply to me at all. Doing all the same to stock C2 997 is much more interesting and rewarding process.

So, as of 'track package' talk about Mustang - may be, who knows. I leave it for modern day teenagers to play with. I have no interest spending my time and money on this platform, just do not see any fun in this, sorry.
Again, last time I test drove any Mustang was about 7 years ago perhaps, and it was right after I tried BMW 3 series. Impression after that comparison was so significant that I lost interest to this brand forever and unlikely will change it ever, for me it looked just as a heavy unresponsive wardrobe on wheels with too small rear tires to provide stable traction. If they managed to improve all that over past years, well, I am very glad for Ford.