The next DLC courses will be released on August 4th. The same amount of courses were included in the first wave of this second wave. Sky-High Sundae is a brand new course that is based on tracks from previous Mario Kart games.
There are returning tracks from Mario Kart, Mario Circuit 3, Mushroom Gorge, Waluigi Pinball, Snow Land and New York Minute. Sky-High Sundae is coming to Mario Kart Tour at a later date, according to Nintendo.
In February Nintendo said it would release six waves over the next two years. The amount of tracks in Mario Kart 8 Deluxe will be doubled to 48. The game has sold over 45 million copies, making it the most successful title to date for the Nintendo Switch.
The Nintendo Switch Online + Expansion Pack subscription includes the second wave of tracks, as well as the Booster Course Pass for $24.99. All 48 DLC tracks will be included in that price.
I was a little disappointed by the first set of tracks, which I didn't think were as good as the courses in the base game. Hopefully, with more of this second wave of tracks, they will feel more energetic.