I also read this. Seems it applies to both GT350 and GT350R. It's not surprising for summer tires. Check out some of the tire websites for more thoughts on summer vs. all-season tires. If I were to get stuck in cold temps with my Shelby, I'd try putting the mode selector in "weather."Page 42 of the GT350 Supplement to the Mustang Owners Manual states "We do not recommend using the original equipment tires when temperatures drop to 45F or below."
Communicating with other owners it seems the soft compound becomes hard and you are at risk of losing it if you drive the car hard. Going to attempt to get comment from Michelin.
Certainly something to consider.