While football is the most profitable and popular sport in America, it fights an uphill battle against other pro sports with much longer seasons and much more games.
In terms of business, it would make sense to lengthen the season. Understandably, the number of games will never reach that of baseball, basketball, or hockey, but an 18-game season is better for the sport in terms of long term sustainability.
Nevertheless, as the season gets longer, strategies have to change. As Flock put it, keeping players healthy through the season gets harder the more games that are played, but this just means that balance would take a greater precedence. Instead of depending heavily on one quarterback, teams would need 2 decent ones to stay on top of the league (in most cases).
Obviously, the Patriots only needed Brady a few years back, but when he got injured and missed most of last season, the difference in team strength was stark. Matt Cassel is good, but he's no Brady. If Brady had been weaker and Cassel stronger, their season would've turned out much better.
So, if anything, the emphasis would slowly evolve into more of a team building exercise. You'd still have star players, but injuries would make a greater difference in overall season performance.
