Cage football with no equipment?I think you're right. It will happen gradually, but I've had discussions with other parents about our kids playing football (usually with guys like myself who played football) and the overwhelming response is "No way am I letting my son play that sport." There's a question as to whether my town (pop. 60,000) is going to be able to maintain a football program. They don't have the numbers for a freshman team and half of the JV team is needed to fill out the varsity roster.
And I live in the same town as Tom Brady and Bob Kraft. In fact Jonathan Kraft's 11 year-old son is playing soccer, not football (though I think he's got an older son who plays football). Obviously football's more deeply ingrained in places like Ohio/western PA and Texas, but the argument that "I did xyz and I turned out fine" doesn't seem to gain much traction in other facets of society (wearing a seatbelt, drunk driving, smoking, wearing a helmet when you ride a bike). I doubt football will prove to be an exception long-term. You can play sports which don't damage your brain.
The model for where football might go is boxing. It used to be massive, the only sport which could challenge baseball's supremacy during the Golden Era. It still does good business and is a popular gambling sport. Yet people are less interested in the average boxing card and mostly get worked up over megafights. Olympic boxing has gone way downhill (at least in the U.S.) and nowhere near as many kids get involved with Golden Gloves as they did 50 years ago. Most parents certainly don't want their kids getting their brains knocked around inside a boxing ring. I can see that kind of future for football - big events, less youth participation, generally older fan base, increasingly taking a back seat to other sports. Might be more like a 40-year process than 20.