The most convincing piece of evidence of is a pair of videos posted on various Mustang message boards of a Classic Design Concepts prototype 2006 Mustang Convertible with a retractable hardtop. CDC is the outfitter that produces the panoramic Glassback roof conversion for late model Mustangs in cooperation with Webasto. You can check out the video of the retractable hardtop going up here and going down here. The conversion apparently doesn't touch the trunk's cargo space, instead eliminating the back seat and making the Mustang convertible a true 2-seat roadster. CDC's website makes no mention of the availability of a retractable hardtop conversion, but the fact that a prototype exists says something.
In light of the speed at which Ford is moving to put the Shelby GT into production and the fact that it's working directly with Shelby Automobiles, Inc. to produce the vehicle, the idea Ford might partner with other small companies like CDC/Webasto to produce a Mustang hardtop convertible isn't that far fetched. You can bet we'll be seeking out CDC's display at SEMA this year hoping to see this car in person. Adding the retractable hardtop to the lineup would give Ford a dizzying array of Mustangs in its lineup. Considering the Mustang's impressive sales performance, that hardly seems like a bad thing.