Commentary in the WSJ
The mere suggestion that the league's booming popularity could ever be vulnerable to a slowdown would be scarier outside of league headquarters. The companies who do the most business with the NFL operate in industries that have been disrupted by competitors and new technology. Those companies are clinging to the NFL and their massive fanbase as they were a lifeboat.
The NFL, as it stands, props up TV networks, who have been broadsided by Netflix, among others. If viewership dipped, they would no longer be able to hike up affiliate fees to local stations, which give them a dual revenue stream, along with advertising, and are almost directly tied to football. Those inside the industry say this sort of chain reaction could—no exaggeration—cause the downfall of the entire television industry. Television networks would have to find something that could possibly deliver 17 million viewers on on a consistent basis. Spoiler alert: They can't. The power the league has over broadcasters was clear when CBS took their popular Thursday Night comedy lineup and pushed it aside as if they were cable access shows. "The Big Bang Theory" is now on Mondays. The NFL anchors Thursday nights. And Sundays.
Everyone agrees that if the NFL took a hit, there's no logical replacement. The Pro Bowl, the league's afterthought of an All-Star game, draws better ratings than nearly all baseball and basketball playoff games.
(hat tip to Brian)