Update: there is now an improved version of Volcan Island in the addons and while it is definitely an improvement from the original, there are two problems. First off, the terrible sand textures still haven't been replaced. Second, some of the rock placements just feel unnatural like someone just placed a bunch of random rocks next to a volcano, though it's probably better off that way. AI works very well and the track feels a bit more exciting, although I do think revamps should focus on actually improving the graphics (less polygonal curves, smoother roads) and quality of textures instead of just simply adding details, although for a track like this it wasn't needed as much.
I'd probably move both Volcan Island and Shifting Sands up a few spots in my ranking since they have been improved on.
Green Valley will inevitably return since Sven is already working on it. Alayan said something about Paradise Peaks could return if given graphical improvements. While I do like the music and atmosphere, I think the driveline is somewhat repetitive and Lost Chasm would be a better choice if it didn't have some of the worst quality textures.