Fool's errand, trying to guess and predict and all that, but why not be a fool? And I think these sound neat.
I think of the 2008 Beijing Olympics opening ceremony with that huge video screen floor and wonder, Could you make a football field with that? Or, hey: astroturf and other artificial surfaces where the blades of pseudo-grass work like pixels! Even better! I picture the end zones changing during the game to be the two different teams' logos, depending on who's driving towards that end zone. Yeah, the Giants, say may be playing in Seattle's Qwest Field or the Jones Dome (really, St. Louis fans should start calling it that), but they could be driving towards their own name; that's motivation! And the field could also have that animation that TV coverage of the NFL now adds, the down line and the line of scrimmage and the scribbled-on-the-screen breakdowns of the plays that John Madden does, but it'd be visible to the people in the stadium, too. (And by then, it'd be Cyborg John Madden, his fragile human body protected in a Terminator-like body but his football-knowing mind still able to analyze how everyone's playing!)
And picture this: a stadium projecting a football game onto its field, with the whole team and the refs visible as holograms. So the 49ers could be playing the Bears in Chicago, but San Francisco fans actually in San Francisco could go to their stadium and watch the game as if it's happening right in front of them. Automatically that's double the potential attendance of a game, and the NFL (which liiiiiiiikes making money) would like that.
* Footballs with little engines, for extra kick in the throw. Like warp drive for the pigskin!
* Instant replays projected above the field, in 3-D, not just on a Jumbotron. You're in the stadium, looking down at larger-than-life football players who are then projected literally larger-than-life!
* Skeeball-like goalposts, where field goals or points-after-touchdown get different amount of points based on where between the goalposts the kicker managed to kick. You'd have sensors detecting where the ball went between the posts, and the air between the posts would light up like Star Trek force fields with a dot where the ball hit. See? it could work!
* 3-D play, like Quidditch. Rocket boots! Anti-gravity generators! Balls and players bouncing off the roof or the blimp!
IMAGINE THE POSSIBILITIES.