heres some ideas I have though I cant art, so if you like them maybe you could art them;
Stream of consciousness; - through-composed music (ie no loops). allgear
Amen Sin 3; remix
Etchmodit; 4k, 8k, drawn waveforms only
Cacophony; Dual Stage like detroit. First stage is people submit something in the 'vocal' format. Second stage is remix those vocals only to make a track. You dont have to keep the 48hr rule though for making the track if that makes it easier to create the battle.
Its game jim, but not as we know it; tic80, doom, boom, html5
Make a sci fi game or level
Four Affinity; Only 4 colours allowed, draw a creature. Pixel/draw/visuall
Visual Novel; pc9x-01
Piano Demo; Make something that sounds like it would be the demo track of a piano. MT-32, midi, musescore
Chipscape navigator; make using only your browser. baby-k, jummbox, pixel, draw, wildchip, html5 (if there others feel free to add)
MPTone; make use of a different microtonal/xenharmonic scale. OpenMPT
Soundchip R&D; give the design specs of your ideal soundchip. This can also make use of some of the more soundchip-speculative software out there. wildchip, sunvox, jummbox, klystrack, bytebeat, puredata