I did the survey when it came out. I was pushing for the Coyote-powered S197, but I can see the argument for the 4.6L being a less-costly buy-in. But that's because the newest 4.6L cars are now 13 years old, and here in the Northeast that means rust damage is a real concern when shopping. Also, the Coyote-powered cars got some upgrades that would help on track, e.g., larger ball joints, stronger spindle that was only on a few years of the 4.6 cars; maybe the spec rules would allow upgrading to those? The NC Miata production run is pretty much the same as the entire S197 run across both V8 engines.
The 4.6L cars may make sense cost-wise right now, but you really need to look 3, 6, or 10 years down the road to see if eligible cars will still be readily available in reasonably good condition. In Spec Miata, they balance the 1.6 vs 1.8 engines with restrictors and weight. Do people think you can "cripple" the Coyote-engine cars with inlet restrictor, weight penalty, and maybe reduced tire width so a 4.6-engine car is competitive, without completely stripping the "joy of racing" out of Coyote car?
Jim Farley did an interview recently in which he talked about Mustangs in amateur racing. He primarily discussed the Dark Horse models and their new IMSA class, but I think SCCA (and NASA) could partner with Ford to develop a spec kit for "Club Spec Mustang" that includes suspension and mild power mods. Unfortunately, it looks like FRPP is discontinuing S197 parts as stock is depleted, even Coyote items. Hopefully a project like this would entail a new production run of some of those parts.
I'd really like to see Ford develop a specific tune for the class and sell it with the Track Cal hand unit. Any questions that someone's running a "cheater" tune? Tech can flash the spec Ford tune into cars at will.
Spec Miata changed from Bilsteins to non-adjustable Penskes a few years ago. I think the Penskes are $340 each through MazdaSpeed (Mazda's equivalent of FRPP, though they offer discounts to competitors - hint, hint Ford). Imagine a "Club Spec Mustang" suspension package that uses NA Penskes that are valved specifically to the spring & ARB rates in the spec suspension package.