the big question is, are they watching it just because it's the world cup or are they watching it because they like the game of soccer. my guess is that it's only because it's the world cup, which only comes around once every 4 years
I have no delusions about the overall popularity of soccer in the US, and I know that a good chunk of the audience is because it's the world cup. Looking at regular season average viewership vs the Super Bowl in American football, about ~80+% of the audience is watching strictly because of the event, not because of the game (18 million viewers on average per reg season american football game. Record highest viewership 2013 of any single reg season game 27.5 million Fox Sunday 4pm game. vs. 111million viewers 2014 super bowl)
I also know that in the past World Cup viewership numbers have not translated to viewership of MLS (which, until very, very recently has not even been close to par with other leagues around the world and still isn't IMHO, just getting better).
What I am really looking at is the trend. US soccer audiences are up 40% over the last 4 years which were up by 30% over the previous 4 years which were up by 25% over the 4 years before that. The trend seems to be a rising exponentially with the standard 4 year bump.
Overall, soccer viewers (paid attendance and especially TV audiences) are decades younger than baseball. 50% of baseball TV viewers are over 55 years old (Dead to most advertisers). About 76% of baseball TV viewers are over 34 years old (nearly dead to most advertisers). The number of those under 18 watching baseball on TV in 2013 was statistically 0%. And the TV audience for baseball in 2013 was 82% white men according to Nielsen demos. Compare that with TV audiences or soccer MLS soccer (again, like comparing AA baseball to Majors when talking about talent level to most other leagues around the world IMHO). About 15% of the TV audience is under 18 years old. Over half the TV audience is under 34. 90% of the TV audience is under 55. Essentially, advertiser gold!
So you would think that all the younger audience is all immigrant and his Hispanic. Nope. The demos mirror the make-up of this great country racially/ethnically, but skew male (65/35). The male skew in TV audiences of MLS is still much less than that of MLB.
My point is that soccer in the US beyond the high school level seems to have taken root. It's been slow, but the trend is there. It has been building for 40 years with fits and starts. But the trend continues to grow with a steady increase in that rate of growth.
I guess the real tale of the tape will come next year.