I would strongly recommend expanding the stepper to include a loop point. That way you could make looped textures with a defined attack (setting loop step to, say, 2 would create 1234567823456782345678, etc), or you could create a one-shot by setting the loop point to 8 (12345678888888, etc). The latter would open up SID style kicks and snares, not to mention the classic "octave blip", where the first one or two frames are played an octave higher than the rest of the note (or play on a different wave, etc)
At a push, I'd also recommend at least 12 steps, though I think you could squeeze out drums with only 8 at a push. 16 would be ideal
The stepper is also preferable for volume envelopes, so expanding the number of steps would open up possibilities here. A rough envelope made from discreet steps sounds infinitely more "chippy" than a regular, smooth ADSR. The difference is night and day.
Adding that functionality would render the need for a drumkit moot. I'll personally supply some drum patches in that case.
