I think football has two major problems that will require change.
First, football is a dangerous sport. There is mounting evidence that football, particularly at the highest level, causes brain damage.
This could become a hit to popularity if fans lose interest in watching concussions. As parents grow concerned, fewer youth football players likely means fewer lifelong fans.
Second, college football is a financially lucrative business built upon players restricted from earning salaries. Division I football players receive scholarships covering tuition, housing, meals, etc. For most, this is a good deal. But some players are vastly underpaid. After being drafted first this year, Baker Mayfield will earn upwards of $8 million per year in the NFL. How does that compare to his scholarship just a few months ago at the University of Oklahoma?
At some point I believe this will be widely regarded as unacceptable. Players like Mayfield bring in significant revenue to their universities and to the NCAA. While student-athletes are not allowed to bring home any of the cash directly, one devastating injury could take away their future as professional athletes.
A related criticism of this arrangement is that college football (and basketball) have become so big they are major distractions to universities. In some cases, star student-athletes are treated differently in the classroom and in university discipline systems. Football coaches are some of the highest paid government employees in many states.
Where is this all headed? First, I think we will see professional football careers shorten. Long-lasting head trauma is a result of repeated blows, which can be minimized by playing football for fewer years. Second, I think we will see an uncoupling of major sports from universities. Most major football programs have enough brand loyalty to continue on divorced from their (now former) university. Third, I think these two trends will merge towards a unified system of professional football. Most players will play from the ages of 18 to 25 and we could see a future matchup between the Oklahoma Sooners and the Cleveland Browns.
There are obviously other common grievances with football. Many fans think the football rulebook has become too complex. Some fans think the NFL is anti-patriotic. Cord-cutting could be a financial risk for football. But I think only the high risk of concussions and the student-athlete arrangements are existential risks to the current football system.