Ford wants a halo Mustang they don't have to pay Shelby America to license. A street version of the racing car makes the most sense. I would look for a street GT4 or GT3 before I hold my breath on the Shelby.
The Ford Performance Cobra Jet drag cars have been equipped with Whipples for years. The FP 700 package for the F150 is a Whipple. The Whipple kit is a direct bolt-on, Roush requires you to cut flanges off the block.
Tied selling is a federal crime. The FTC oversees the prosecution of it on the federal level. Your state's AG will bring charges on a state level. Tell the dealer you want a copy of the sales agreement to file with your state AG. They will change their tune quickly.