In the future, the retailers would be out of the loop as broadband speeds increase. But, currently, the majority of Americans don't have the broadband speeds to download a 50GB game. They could work an odd job to get the gas money, drive to the store, d/l to SSD, drive home, make a sandwich, and eat, way before the game would be finished d/l over the broadband connection.
In the model I was thinking of, retailers would have a server kiosk with enough storage to hold lots of games and the only speed issue would be disk transfer rates.
If there's a one time upfront cost of an SSD cart that you would recoup later from lower priced games (which may or may not be possible due to the cheapness of disc media and expense of transportation), I see that it's possible people would adopt. Lots of people don't mind buying expensive memory sticks for their PSPs for movies and homebrew.
They've talked about a model like this in distributing movies for a long time (where you would get your movie burned to disc on the spot), but yet it's never come to pass.
Problem I see with it, when you buy a DVD you want your nice pretty case and box art too. So you're going to have to print the art, and keep a supply of blank cases on hand..so you're not gaining any physical inventory at the store level...I dont know, there's just problems with it.
Immediate problem I see with "DL from a kiosk" for games is, are you going to have a separate flash cart for every game? If not, then you cant own multiple games ready for instant play at once. For example, lets say I want to go buy five new games..I either need a really big flash cart (expense..and now what if I want to buy twenty games? Or I'm rich and I want to buy fifty?) or I need five separate flash carts. (Although, most consoles have HDD now, so maybe you could just use that instead).
I think DL at home is more likely going forward. Someone threw out 50GB games a minute a go, but there's like one of those (MGS4). Other than Blu Ray, most are 4-6 GB.
There's competing forces on game (and movie for that matter!) size right now..the trend toward download (XBLA, even a few full games from PSN) will tend to put a premium (and pressure that direction) on small file sizes. Even as Blu Ray says "Hey devs, fill all these GB's up, please!". It's similar to the movie market, where netflix download wants to give you a tidy file size at a lower quality, while Blu Ray wants to spare no expense. In audio, we know small file sizes (MP3) easily won out..