Hmm… a compo…
The 4k competition was pretty much fun, despite the fact, that I hadn’t finished my entry (animation + sound fx(!) | 3733 of 4096 bytes used).
Maybe it sounds odd, but it was way too time consuming. The same game in 16k would be done in 1 day… and it would run more than 2 times faster. However, I learned a lot and it was kinda fun after all 
Therefore I suggest that it shouldn’t be too restrictive.
64k (65536 bytes), at least one sound, Java2D… would sound like fun imo 
Or let’s say <=512kb and the size of “default” libs (lwjgl, jogl, jinput, xith, joribs etc) doesn’t count?
Several categories just doesnt work I guess… the community is a bit too small for that.