Being real doesn't mean anything. The "real" big companies and corporations are the people who would play April Fools jokes because it would extend and reach a lot of people in the process, whereas smaller businesses and such wouldn't because how many people would really see it? Come on, now.
Gameplay? Doesn't provide enough proof. Who says they didn't just take a normal clip and speed it up a bit? Who says that they didn't hire some amazing video editor to make it look fast. Nintendo is certainly raking in the $$$ (and is loaded) to do so. Like I said in my first response, I can't prove that this completely is a joke, but since it was posted on April 1st and the fact that for all these years, the Mario Kart franchise has always had three speed modes (or whatever you want to call them), it just seems very off-putting to me to just all of a sudden have a 200cc.