Renoise supports mono and stereo, but in my mind I imagine a third speaker and Renoise should support it.
A new button next to Maximize that turns Renoise into a 1x1 pixel window.
New device called “Signal Leader”. Instead of following the signal, it does the opposite.
The PhysX device, opposite to the cabinet simulator but does rag doll physics for notes.
The Hi-Fi device giving your tunes that authentic 70s disco sound.
A “compiler”-option so that all the empty spaces in a song will be deleted (ie all notes, no blanks).
A selection of soothing background noise to choose from. Sea, wind, whitenoise e.t.c.
I really like that idea,
I read on a physics forum somewhere about trees emitting a type of noise.
My bad idea:
A mirror x2 function, this turns everything backwards and upside down for using a mirror above your display, so we can lay on the floor or bed? and see renoise while doing other things. (like sleeping) 
Quantum Time Compressor-Plays all sounds in track at once, thusly transforming a 5 minute work into a blissful 1 second cacophony, perfect for todays time starved society.
BTW: Some funny posts here, you guys have made me smile first thing in the morning, not a bad start to my day! 
LOLS for all the above!
A function that turns my girlfriend into a rap & r&b one hit wonder diva whenever I plug her in.
Vsti version?
edit: worse - rtas version
Piano Lol
Add nibbles to Renoise. Eventually remove all the audio features to focus on nibbles due to public demand.
In addition to Send Tracks and the Master Track, please add a Twitter Track.
I want Nibbles 
Random porn popups that link to pogo.com
That’s a great idea!!! Which means that this thread is also a good idea, which was originally not so.
The next version will include a popup blocker, also a Banner Ad Track.
please, please, a build-in automatic facebook friends adder!
I don’t need that feature, i can already assign a track to my third speaker if i desire.
Hell i can even configure to output 5.1 on my soundcard.
I bet there are even 7.1 ASIO configurations possible.
I’ld rather had a feature where I sing in my song, and Renoise magically arranges the whole slew and background instruments around it.
Bad idea (more of a bad habit, really): spending too much time on the Renoise forums when I should be working 
karaoke mode