I highly doubt the cost of a big release game will ever fall. This is excluding indie games, xbl games, etc. Even if this no second hand thing is implemented, it's up to the publishers and not the hardware manufacturers to price their games. Of course, there's a cartel sort of arrangement where everyone ends up with the same price, but there's no way the big pubs are going to drop prices on AAA titles. Ever.
People were saying the same thing a few years ago when the online stores started getting traction. XBArcade, PSN, Steam, etc.
"cut out the middleman, savings for everyone, more profits to the devs, woohoo!!" 2 out of 3 aint bad I guess.
There's been no drop in cost whatsoever, and most games are still higher priced on the online store than if you were to go to a retailer. That said, I've bought quite a few games over XBL that I don't regret purchasing for a higher price. It's the convenience factor that makes it worthwhile.