Here's my predictions for the remaining retro tracks not counting Tour cities or nitros.
1 SNES
Choco Island 2 / Ghost Valley 2
I feel like it's one of these two themes. The track number I don't have strong feelings towards, just went with 2 for both. After seeing Snow Land I'm not sure about Vanilla Lake as we will probably have enough snow themes.
3 GBA
Sunset Wilds
Cheep Cheep Island
Luigi Circuit / Boo Lake / Broken Pier
First two are obvious as they're in Tour. The 3rd one I know Luigi Circuit is speculated for Tour. I didn't pick Yoshi Desert as I feel like there will be enough desert tracks in the BCP and we could be lacking in ghost tracks hence Boo Lake / Broken Pier.
4 GCN
Daisy Cruiser
Waluigi Stadium
Dino Dino Jungle / DK Mountain
Mushroom City / Mushroom Bridge
Mushroom City/ Bridge is based on Tour datamining. Picked 1 of them cause they both cover a similar aesthetic, same with either Dino Dino Jungle or DK Mountain.
2 DS
Mario Circuit / Luigi's Mansion/ Delfino Square
Airship Fortress
I think Airship Fortress is a lock, but don't know about them doing Luigi's Mansion for the 2nd DS track. Delfino Square is a fan favorite, and I could see us getting another Mario Circuit besides from SNES hence the DS version of it here.
4 Wii
DK Summit
Koopa Cape
Maple Treeway
Rainbow Road
The first 3 are in Tour and that final track in the Spiny Shell Cup feels made for Wii Rainbow Road.
2 3DS
Rock Rock Mountain / Bowser's Castle
Rainbow Road
3DS Rainbow Road is a really popular track from MK7 and fits as a cup finale. The other one I'm not sure on but I'm feeling either Rock Rock Mountain or Bowser's Castle would fit. Could be Bowser's Castle so we get at least 1 of them in the BCP, as the only other obvious Bowser's Castle would be GBA's and I have a feeling they won't pick that iteration.
I think i'll follow your lead and give my current predictions for the remaining retro selections:
SNES: 2
- SNES Mario Circuit 3
- SNES Ghost Valley 2/3
Before the Wave 2 reveal I was on-board with Vanilla Lake 2 being the second SNES course, but Snow Land blindsided me in multiple regards. Now I think we'll be getting one of the Ghost Valley courses; all of them are coming to Tour eventually after all. Ghost Valley 2 was even officially announced for Tour in 2020 but has bizarrely disappeared since, with 3 datamined since. One of the two will make it.
N64: 2
- N64 Choco Mountain
- N64 Kalimari Desert
If the prefixes are 100% accurate, then we're done here. Shame, because I would've welcomed rescuing Koopa Troopa Beach from Tour too; or another returning course that has been remade before like Banshee Boardwalk or Bowser's Castle.
GBA: 5
- GBA Sky Garden
- GBA Snow Land
- GBA Sunset Wilds
- GBA Bowser Castle 2/3
- GBA Lakeside Park
Sunset Wilds was on the datamined banner, so we may as well tick that one off too. I think one of the Bowser Castle courses will have to come over eventually, and I vote for any of them but the first. 3 isn't in Tour yet, but there's reason to believe at least one more GBA BC is coming to the game and it was remade in Wii prior (where it was decently well liked, I believe), so I see it as possible. As for the last GBA course... i'm really not too sure. Tour has Cheep-Cheep Island, Luigi Circuit and Yoshi Desert to pick from; but there's also the posibility of another wildcard choice, so i'll try to will Lakeside Park into reality.
GCN: 4
- GCN Waluigi Stadium
- GCN Daisy Cruiser
- GCN Mushroom City
- GCN Dino Dino Jungle
Gave my reasoning for these picks above, so I don't need to repeat myself. You could swap Mushroom City for Mushroom Bridge or Dino Dino Jungle for DK Mountain, but I think the other two are locked in.
DS: 4
- DS Shroom Ridge
- DS Waluigi Pinball
- DS Delfino Square
- DS Airship Fortress
Here's another one where i'll go against sense and Tour datamining in favor of the track I really want. Airship Fortress is guaranteed, and realistically Luigi's Mansion should be the other DS course, but I really want Delfino Square to make it. There's nothing really pointing towards it; spare an interactable gondola object like the ones that appear in Delfino Plaza (didn't exist in the original course or Wii version, but could be added for Reverse / Trick versions perhaps?); but it's the one I want to see the most. Expect to be wrong though.
Wii: 6
- Wii Coconut Mall
- Wii Mushroom Gorge
- Wii DK Summit
- Wii Koopa Cape
- Wii Maple Treeway
- Wii Rainbow Road
All of our datamined info makes this selection the easiest to place; three of the courses are on the datamined banner, and with the Spiny Cup ending in a Wii course Rainbow Road is the natural best choice to fit. Tour will have Dry Dry Ruins to pick but it seems they'll be passing on that.
3DS: 3
- 3DS Toad Circuit
- 3DS ???
- 3DS Rainbow Road
Rainbow Road is a lock based on the banner and Moon Cup prefixes, but for the other 3DS course coming in Wave 3 there's just too many options available. Tour already has every 3DS course besides the Wuhu tracks available to pick from, and those two are coming eventually as well; so there's no easy choice to make here. I'd personally want to see Shy Guy Bazaar, Wuhu Island (both Wuhu courses combined) or Wario's Galleon; but Alpine Pass feels like a possible option too.
I'm also holding out hope that perhaps Wave 4-6 will be shuffled around a bit (it is weird that they all feature GCN and Wii courses in the same spots each time), and that perhaps two of the blanks in Wave 6 will end up being retro courses after all. Would be nice to open up another spot for N64 and 3DS; as both of those games being exhausted by the end of Wave 3 with so few tracks is a weird outcome.