Nice to see the ideas for improvement...
I went through the pages and compiled requests that make general sense. I am very sorry if this isn't exactly a "most requested features" list, but this sticky could utilize it, I think:- Fullscreen settings are preserved, along with the graphical options.
- Photosensitive seizure warning a switchable setting
- Account Information-changing feature
- Versus Mode: split-screen
- Dual XBOX360 controllers support/common HID controllers support
- Game types (Mono Double-Vision, Vegas Elite, custom game modes)
- “Crowd” sound effects return request
- More/custom visual scenery in-song
- Music length limitation increase (limitation removal would cause issues)
- Last.fm radio selections for playing songs
-
Tagging: + consider song length & a graph analysis (with deviation factor)
+ consider other tag info (album info is suggested)
However, I hear this issue will be treated with MusicBrainz.- Daily challenges
- Store scores locally, on file, for reference
- Customizable controls
- “Song first, ship later” selection order to ease character transitions
- Continuous album play
- Savable playlists, and the ability for others to view them respectively
- Visual icon next to songs in the browser indicating they have yet to be played via Audiosurf
- Option to change “dethroning” notification to an in-game feature
- Viewable “pre-loaded” folder
- Several audio format support requests (Musepack, APE)
- In-game changeable tags
It's a sizable list, but I thought I'd help and compile stuff. I know I missed a good number regardless. 
Time will tell how they're treated... good luck, developers! Great game!