I smell a lawsuit on the way. A group calling themselves Mushroom Rally USA has announced a series of go kart racing competitions across the USA (with some international events as well), and they are not even attempting to be remotely subtle about the fact that they're trying to cash in on the Mario Kart brand. All of this, of course, without any affiliation with Nintendo.
The group's website advertises that you can dress up as "your favorite characters" (while a video clip clearly shows Mario-related costumes) and compete for stars in a series of races across 16 cities. There will be games (unclear exactly what this means), prizes, a DJ, and more, and the winners of each event will compete in the finals in Las Vegas.
While this sounds like a lot of fun... it also sounds likely to get shut down if Nintendo has a say. The website is blatantly using Nintendo-related properties to advertise, which they apparently believe is fine thanks to a brief notice at the very bottom of the page stating that there is no affiliation with Nintendo.
That disclaimer likely won't stop Nintendo from taking legal action, just as they did with a similar go kart service in Japan that blatantly ripped off Nintendo IP. They were eventually forced to pay out ¥10 million (around $88,000) and stop using Nintendo-related branding, but the legal process took around a year and a half.
Source: Mushroom Rally