For the soccer doubters, who think and or want soccer to go away for 4 years, I think this is the tipping point the US has been waiting for - it really is the perfect storm for a growth explosion.
1. This team, and this WC, has captured the attention of a lot of, relatively young fans. The enthusiasm shown across the country, used to be seen in small pockets, but now those pockets are spreading.
2. The amount of high-level professional soccer that is available on TV has never been higher, and people are tuning in in record numbers. One of the reason the WC has been successful, beyond just the success of the US team, has been the number of household names that people recognize from watching the EPL, La Liga, Bundesliga, MLS, etc. The WC coverage will feed right back into the club season that are starting up in August. It is almost self-feeding at this point.
3. Between now and the next WC in 4 years, there will be an unusual amount of competitive USMNT games - Gold Cup in 2015, where we will field a competitive team, rather than all B-squad players, Copa America which will include the South American powers playing here in the US will be in 2016, The Confederation Cup, which the US is in good position to attend, will be in 2017, WC qualifying will take place in 2016 and 2017, plus a number of friendlies - probably against traditional European powers. In short, this happens to be the one time-frame where the US can really capitalize on its popularity because it won't shut down for a couple of years.
4. Fathers and sons are now partaking in watching soccer in numbers that we have never really had. My dad never enjoyed soccer, despite the fact I played most of my childhood. I watched games with my kids, and they were excited about it. That is where it will translate to a wider audience - kids are growing up with soccer on TV and watching it the same way I grew up watching football or baseball with my dad.
I know this has been talked about for decades, but you can really start to see the evidence of the tipping point right now.