I don't think what he said was really that crazy.
The NFL was the perfect weekend event. Sundays during the Fall/Winter when the weather is crap and no one is doing much, sitting around watching football is perfect. You only needed to pay attention Sunday/Monday night and that was it. It's not like MLB/NBA/NHL that you have to dedicate a few days/nights a week to watch your favorite team play. Now with the Thursday night games, they're starting to oversaturate the market. Simple suppy and demand. The demand for football was so high because we could only watch games 1 day a week and then on Monday night. Now we're up to 3 days a week and then towards the end of the season, we'll see Saturday night games.
The Fantasy Football angle is also important. The guys I play fantasy football with don't like playing fantasy baseball or basketball because you have to pay way more attention since there are games every day. That's why fantasy football is so easy for casual fans to pick up. You really only need to pay attention to your team on Sunday mornings. Now with games on Thursday, you're asking people to take dedicare more of their time to football.
Also agree on the concussion front. As concussion info gets more and more detailed, I could see parents trying to steer their kids away from football. Why play football and get constantly beat up when your kid could play baseball, basketball or soccer?
Another thing is that the NFL has essentially priced out the average fans from going to games. To take a family of 4 to a football game anymore is about the cost of a week's vacation. For example, to get into a Redskins game and sit in the lower level, you'd pay about $125/ticket. So for a family of 4, you're paying $500 just to get into the game, plus another $50 just to park your car. Then you're paying $9 for a beer, $5 for a soda, $8 for a hot dog. Before you know it, you've dropped $600-$700 just to watch one football game with your family. That's nuts.
Is Cuban right that the NFL will implode in 10 years? Probably not. But I don't think he's too far off.