Tbh I don't think it's going to be anything special. It's probably a Jungle Tour with Lakeside Park and some returning retros.
Speaking of which, I saw a post on the Mario Kart subreddit the other day that got me thinking. They were predicting Vancouver Velocity for this Wave due to the lack of fan favorite courses currently rumored for Wave 5. We don't have a popular returning retro for the Wave yet (Wave 1 had Coconut Mall, Wave 2 had Waluigi Pinball, Wave 3 had Maple Treeway and 3DS Rainbow Road, and Wave 4 had DK Summit and Waluigi Stadium), and three of the four retro courses everyone is predicting are pretty simple tracks (Sunset Wilds, Mushroom Bridge, and SNES Bowser Castle 3). I'm starting to wonder if we might see one of the simple tracks pushed back, and one of the retro courses from Wave 6 brought forward.
What if we get DK Mountain in this Wave?