Although I'd bet it has been mentioned before, I have an idea, and please post your thoughts on it.
3 years ago, I was playing a football game with a friend. We discussed the possibility of being just one player, not being able to switch players, and being able to realisticly perform football-related actions on and off the field. This would include a dynamic player progression and rating system, where players really don't actually have "ratings" and they just are players with stats, who can actively develop and change between games (Take HIGH HEAT BASEBALL for an example). I would also like the attachment to that once player when playing with him for the entire career (maybe even in college, although that's an unrealistic request because of licences).
At that time, we quickly trashed that idea, because we agreed that it would be impossible, and there would be no way a video game could be able to pull that off. But times have changed. With the innovation of FPF in ESPN NFL Football, playing with a single player is a reality. Although I would love to be able to look up and down (and not just sideways), and to be able to do that quickly and effectively, it's a true possibility.
There are many things holding this idea back, but I think that in 3 or 5 years (at the rate that technology is going now), when real voice-recognition, more realism to make it feel more like life, a much better collision detection system and effective AI, it could happen. I'm looking forward to it. Although it isn't a very economical decision because the only people who would buy a technologically superior, and therefore unbelieveable expensive game would be a diehard football fan, who has XBOX 3 (It's bound to happen), includes about 1/1000 of the population. I'd love to see this in the future. I belive that human-computer interation is really the future.