(I hit the text limit so the other 3 ideas are in a second comment)
1 - Ultimate 10
Song: Ultimate Destruction by TMM43
The level progressively adds elements from each update, beginning with the first few seconds of the scrapped main level before having original gameplay.
2 - First Demon of This
Song: First Town of this Journey by Camellia
This level has a pixel fantasy theme that travels through many old-school JRPG inspired locations, beginning with a forest before entering the song's namesake. The difficulty of this level would be on the lower end of Easy Demons.
3 - Jamasareta
Song: TBD
An accessible -reta level (around a minute or less), featuring fast-paced, flowy, heavily synced, yet readable gameplay. It probably will be a Medium Demon or easier in difficulty. The appearance/deco, depending on the song, will likely take after its music video.
4 - Behind the Scene
Song: Moonlight Sonata (Mv 3) Remix by meganeko
The level takes heavy inspiration and influences from bli's Change of Scene, having a "disaster mode" activate when you hold a dash orb for too long at the start. This is a "journey to many places" that goes through a city, a beach, a volcano, and a laboratory. The "disaster mode" adds a tropical cyclone into the background of the city and beach, an eruption from the volcano, and visible damage to the laboratory.
5 - Nasty Nasty Spell
Song: Nasty * Nasty * Spell by Camellia
A spooky effect megacollab, having many effects in a Halloween color scheme. It's something along the lines of Viprin's Quaoar, but nowhere close to its difficulty.
6 - Explore the Core
Song: Explore the Core by DJVI
A 1.9 RobTop style level with an emphasis on asymmetric duals that use two different game modes at a time.
7 - Tarden Infinity
Song: RGB by Yoasobi
As the name implies, many aspects of Tartarus, The Golden, and SWI, despite the song lyrics not actually being reflective of any of these levels.