A playable Eggman.
Springs that can be picked up.
Make scripts case-insensitive.
Make a CSAY/CSAYTO command for the server that CECHOs to all of the clients.
Editable whirlwind shield height.
Passive wait command for scripts.
Sonic 3-style save games.
Emerald Time Attack option once all 7 emeralds are obtained.
Make the BAN command put all of the bans on a list (text file?) so that bans last longer than just one game.
Ability to BAN via IP address.
UNBAN command to unban just one person rather than everyone.
Ability to assign point values to an enemy in a SOC.
Underwater-dwelling Buzz-like movement code.
Joystick deadzone option.
Ability for music to play seamlessly between levels if the music is the same, like in Knuckles Chaotix.
Ability to set THINGs for Sonic/Tails/Knuckles, like the skill level bits.
Bosses that don't activate until you're close to them (sight distance threshold).
Ability for enemies to have generalized multiple HP.
Allow jumping, spinning, and spindashing to have different sprites.
Ability to have rolling demos for the title screen.
Icicles. Upside down spike with a blue tinge that falls when you get close to it and then shatters or sticks to the ground.
Breakable blocks in Mario mode.
Ability to make other objects act like rings.
Green flickies and have them change color to the player who freed them.
Option for non-music-changing Sonic CD-style drowning.
Option to play an SFX instead of music for 1-Ups.
Console command to re-register with the master server.
Personal profile for netgaming that will show your ties, wins, losses, most # of people you played with in a netgame, best win(by how many points), worst loss, etc.
Spectators for all game modes.
When you save a game with wads, it should automatically load the wads the next time you load that savegame.
Buttons that pop back up when you step off of them.
Linedef executor triggers that work only for specific emeralds.
The option to have Tails follow Sonic around in single player.
"Raise/Lower floor/ceiling by line" linedef executors that gradually accelerate to their specified speed.
It would be nice if slime balls floated on top of water/lava/etc.
Separate sprite frames for Super forms.
A linedef executor that checks how much time has passed in the level.
A separate animation for thokking.
Ability to paste an IP Address from the clipboard, or paste into the console.
A "dir" command for the console.
A chasecam toggle button.
Option to set translucency of the console.