Very little impact, if at any.
Well, let me stop and rewind a second. I think it will have very little impact as far as turning new people on to the sport, if that's what you mean. You are not going to see up-ticks in new people coming out to the local track, IMHO.
This is because:
A). What they are seeing on TV is not the kind of sport that would entice a beginner to say "wow, yeah, I want to do that!," or, "I want to get little Johnny into that." (aside from daredevil types and Richard Branson). To say nothing of the fact that, even if Richard Branson were to show up, there is no place for him to take his day-one bike and blaze down the SX hill (probably a good thing).
B). If the coverage is like last time, the announcers will be calling it "BMX Supercross" (which it is). But if you are a "never-heard-of-it-before" fan sitting in your living room, and do a Google search for "BMX Supercross" you are going to find some sporatic content and YouTube vids on UCI Supercross (and the Supercross
of the Bill Ryan variety, so I'm stoked for Smilin' Bill)...but nothing...NOTHING that makes the connection to the fact that there is a whole parallel universe of "Classic" BMX racing at a track 30 or 40 miles away, that IS beginner friendly (well, moreso than an SX track).
That said, you might see an up-tick in awareness of the phrase "BMX" at the water cooler on Monday the 13th. And there is a slim chance that corporate types (aka potential sponsors) who fancy themselves the "cool guys" out of their bunch, may also take notice. Every little bit helps in that regard, so I'll take it.
As Carl said, if it makes people at the local Little League game stop saying "you do all those flips and tricks?" and makes them say, instead, "wow, you race down that three-story mountain?" It could be considered a win. At least they are talking about the same "flavor" of BMX.
I have heard for the past few years that they would be running the BMX coverage "In Prime Time." Well, in Chicago, at least, it airs at 3PM Central Time (4PM for the final, I believe). Prime time, in the Central and Mountain time zones is from 7PM to 10PM (8PM-11PM in the Eastern and Pacific Time Zones).
Thus, unless you're deliberately looking for it and record it while you're at work...or are super-hardcore and have the streaming coverage up on a device, Joe Six-Pack isn't going to see BMX anyway (unless he's unemployed, and doesn't have anything else to do, that is).
I'll be happy when next week is over and we can get back to "Classic BMX" for two years. I'm stoked for BMX in the Olympics, and can't wait to congratulate the medalists personally, but I'm really here for the Original Recipe.