I have delusions of grandeur. I imagine MTG Forge with undo and when the mouse hovers over a card, all of the legal targets would be highlighted. The user interface would look exactly like a real card table, complete with a red zone for attacking. Each card would be perfectly rendered to look like a printed card, even when abilities were added or removed. And MTG Forge would include every Magic card ever printed, so you could play any format that ever existed.
I imagine there would be some sort of RPG where you begin with a starter deck and then you battle to become the World Champion. You would earn money and cards by competing in constructed, sealed, and draft tournaments. The tournaments would have multiple rounds and you would have to win each one. Tournaments would have random requirements like no forests, or you must use only creatures or islands. Obviously the deck editor would have to support sideboards since sideboarding in tournaments is almost an art form. MTG Forge would keep your Magic rating and it will be close to your DCI rating.
The AI would be very tough. It would analyze your deck and determine the best way to beat you. The AI would mercilessly beat you again and again. Your Magic skills would improve with time, but playing a pro tour AI would certainly make you black-and-blue. The AI will draft realistically and try to cut your colors. The computer might switch colors midway through the draft just to mess you up. It would also excel in sealed deck tournaments. The AI would be good enough to win pro tour tournaments.
Obviously dreaming is easy and programming is hard, but I keep doing both. --Forge