It is likely very much for sale. "Tell them they can't have it and they will fight over it". That has worked in the retail industry for decades, one of the oldest tricks in the book.
Very difficult to consider any Shelby Mustang a "base" model. It is already at the top of the pile. The "R" is just set up differently and has a little more focus towards the track. Personally, I don't want an "R".
Magnetic is a very cool color that does take on a different demeanor with variations in stripe color.
Blue or white stripes seem to work particularly well.