These kind of things are typically kept pretty quiet. Even those who may know aren't supposed to say anything. Interesting though how the period correct 4-inch tube chassis is now perceived as less than optimal. It's been one of the things that's differentiated the Factory Five replica from most of the competition. No doubt the Gen 3 Coupe space frame is even stiffer. But the current design is no slouch. Any chassis I can jack from anywhere on the side and the whole thing lifts is pretty stiff. You can feel how stiff it is when you're driving it too. Personally, I wouldn't consider the Mk4 as getting long in the tooth. It's undergone constant incremental changes and improvements since it was introduced. And the new 2015 Mustang based IRS is sweet.