I guess what I'm getting at is that you seem to imply in the OP that a guy traditionally (to broaden the definition back out) considered a "pocket passer" would be ill-fitted to the Shanahan offense. If I'm reading that right, would it follow that you don't think a Manning, Brady, even an Eli Manning---all guys I believe fit the "pocket passer" label, and would argue are exceptional at finding space and buying time---could make this offense as dynamic as a guy like Cutler?
Just so no one thinks I'm sandbagging here....my ideal QB for today's NFL is a guy like Brees. He can stand in the pocket and go downfield, he feels the rush and can slide to buy the extra second, he can break out and run when necessary, and most importantly, he processes information and gets the ball out, accurately, as fast as anyone I can recall.
I haven't seen enough of Luck and RGIII to form an educated opinion on which would be the better fit in this system or have the greater upside overall....but I do feel pretty certain that Luck, certainly the less "athletic" of the two, would be fully capable of running the rollout plays in this offense. Once there, being a weapon outside the pocket becomes about downfield vision, reading coverages, accuracy and arm strength.
I don't care if my QB is capable of breaking off a 50 yard run--though obviously all things being equal it's an attractive quality. All I do ask in that regard is the ability to recognize and take the occasional 3rd-down coversion run up to 10-15 yards at crucial times. I'm far more interested in his ability to move behind the line of scrimmage when called upon, and then accurately deliver the ball when an option presents itself or get rid of it when it does not.