Those little SD cards (and their relatives) have dramatically grown in storage capacity while still maintaining a tiny size. Cartridges could actually be an option in the near future. Just look at the new laptops that have solid state hard drives. I'm not sure if it would actually happen (and it would definitely increase the cost of game manufacturing), but I do know that I wouldn't miss loading times or disc swapping. >.<

Edit: And "blah" at a future of digital products. I know it's coming, but I'll keep buying music, movies and games on physical media for as long as I can. The digital movement just doesn't work for me...