Thunder Road makes a good point, all of these things would probably increase weight and reduce rigidity especially the T top, while many of these ideas are intresting they probably aren't very practical. I agree a retarctable rear window would not only be a fun feature and reduce drag with the windows open, but how often do you drive with your windows open? and when you do, do you really notice a diffrence in your mustangs performance that justifys the weight increase of the retractable rear window? but anyhow that would be cool to see, but i just don't think that ford would do it, especialy with all of our safety standards today. However I do like the idea of a hatchback, I think it would be a practical and fun vehicle, there really wouldn't be any hatchbacks out there like it. Also it would probably be the most powerfull and IMO best looking car in its class
-Tyler