Personally I would like to see a strong, muscular representation of yesteryear's Boss Mustang. Obviously a step above the Mach, the Boss was a serious street machine even in stock form, especially the '71 Boss 351. Ford has obviously decided to make the Cobra the King of the Hill of the Mustang line so I will follow along that train of thought. If the Boss is designed to bridge the gap between the Mach and the Cobra or even the GT and the Cobra then I would like to see a naturally aspirated version of the 5.4 liter engine sitting between the shock towers. Ford apparently has done all the homework needed to drop a 5.4 in the new S197 platform with the GT500, so I believe a 5.4 in a Boss version should be an easy decision.
I would like to see the car equipped with some Boss exclusive parts, maybe a special intake manifold, valve covers, different exhaust tips, larger wheels, body scoops (a Ram Air hood would be wonderful) - and of course, exterior badging. A T-handled shifter would add a nice touch of "retro" to the interior as would maybe a 3-gauge pod intergrated with the dash (possibly something like Classic Design Concept's '05 gauge pod setup). Being that the Boss was considered both a straightline performer and road racer, depending on the year, solid axle and IRS options could be nice.
Now to the numbers, with the advent of the GT's new rating of 300 horsepower and the GT500's 450+ it seems logical to me that the Boss should be a legitimate 375-400 horsepower offering.
The Boss has a rich history to its name, a name that brought fear to the competition's eyes and wins on tracks throughout the country, so Ford, if you are listening, please do not give us a watered down version if you do plan to release a "Boss"; as a long time consumer and lifelong Ford enthusiast I would rather wait a few more years for a new Boss Mustang to be done right then see a "quick to market" version released for namesake.