The box itself costs next to no more money.
And that extra content is going to be nothing more than a Camp Omega map. They've already announced a Ground Zeroes special edition, so the Standard Edition's aren't going to get anything ... special.
But you're jumping into conclusions still. We don't know that do we now? We don't know the length, we don't know how many missions & side-missions the game will have and we don't know the extra content that Konami & Kojima are willing to offer for those who buy the retail version. Again, let's wait and see. We are getting what we wanted. KONAMI is listening to us. They were not planning on releasing a retail box, they heard our cries and now they are. Give them a break.