There's an AMA over on Reddit from a guy who says he attended a soft opening. He did say that it will most likely take until tomorrow morning Japanese time for him to answer most questions, but he has answered one so far re Mario Kart....
Q:
Someone had leaked this Video over on r/UniversalOrlando
(Link to YouTube - not sure if I can post it here on the forums)
Any chance you can confirm if this is legit and if so, is the whole ride similar to this, or are there physical sets for the attraction as well?
A:
Yes, I can confirm that the video is indeed real.
The ride is filled with physical sets, but you view it through the lens of the AR. Quite honestly, you could still enjoy the ride just looking at the sets without the AR if you really wanted too. That's just how great of a job they did.
So to answer your question, the ride is essentially what you see happening in the video, but it is happening throughout different physical sets.
I hope that is a sufficient enough answer.