Well as it is right now, retailers do take a hit that's why they make money on the used game systems, and older games. You forget how many people are still going to have their 360's and PS3's years from now. New games are still coming out.
Plus gamestop and the likes have found partnerships with other companies to get alternative streams of revenue to hit margin. Gamestop exclusively sell's Madcatz arcade sticks and peripheral's. They have their own gamestop brand of headset's and controller's. Game informer is owned by them, though used games are their bread and butter, they have other ways of getting revenue. Plus I forgot they sell crazy number's of DLC cards, and steam cards. They get kick back by companies when they sign people up for those.
Though Gamestop and Best Buy's and who ever sell's second hand games won't be making hands over fists like they did in the early days of 360 and ps3. They will adapt and offer different things that will bring them money. They sell used accessories and it's pure profit and those won't change with XBOX ONE or PS4. I think they will be fine, people are blowing this out of proportion.
Yes, I am with everyone when they say that their taking away choice from the buyer. But we still will be able to trade our games in. Microsoft Knows that Gamestops are the go to for Predorder's for their systems, New games ect. There's no way they would just shut them out, because they would lose a ton of sales.