The talent pool has undoubtedly increased with the rapid expansion of international interest in football, however the youth system, particularly the NCAA may not be ready to adapt to a more international player base given current funding models.
The fan base is trickier, the NFL has seen above average fan growth both nationally and internationally the last decade at the cost of several other sports. I am not sure this growth can be realistically extrapolated, with Bettman retiring I don't feel it is realistic to expect the NHL to go through 3 more lockouts in the next 2 decades, and likewise I don't see the MLB going through another any time soon.
I feel there are a few markets, especially if they NFL is willing to look into international expansion that could support an NFL team, Toronto, Mexico City and Vancouver would probably be the most obvious places in North America. LA will always be contentious, finding a staple owner group and a facility that is viable long term is going to be challenging, the sad fact is that a large part of the people in LA who have the money to be interesting prospective customers are not from LA and would have little reason to follow an LA based team.