This came up awhile ago regarding soccer vs. US based sports. I said then and I say again now...American football has a life span of 20 -30 years left. Possibly less as this stuff accelerates.
The death of US football will be tied directly to the end of College and HS football in the US. That will come as the lawsuits compile. There is already a $2mm judgement against Pop Warner related to concussions. School districts are sitting ducks with deep pockets. Only a matter of time before a class action ends the sport in HS.
Colleges will eventually lose the whole student athlete nonsense in football making the players employees. They will demand full compensation and the medical care they legitimately should expect. When the dollars that the College system is stealing from players starts going to them and it is the professional sport it really is - how long will that stay in its current form? I'd wager not very long and it is possible that a NFL minor league with 2 teams per NFL club comes into existence. The NFL is creative enough to make the AAA league the Fall Thurs/Friday/Saturday league and the AA a spring/summer outfit for the new young prospects. 8-10 game season from April to June to step on the baseball season opening and basketball and hockey playoffs. Ends just in time for training camp.
Bottom line is the NFL will have to build and maintain the funnel of players it needs rather than relying on taxpayers to fund it. All of this could be very good for baseball if it becomes an alternative for a bunch of kids that otherwise would have been DB's, WR's, RB's, LB's and TE's not to mention quarterbacks.
Of course Soccer could continue its growth and some of those kids could become soccer players. When that happens and the US wins a World Cup - that sport will be forever changed as well.