A slicer would be fantastic!  Controls for duty, attack and mix.  Preset rhythms would be okay (like the
SL-20), doing something like the AdrenaLinn 3 and being able to program 2
measures of slice would be great!  The same program-ability added to
the Harpeggiator would be amazing also.  As was stated earlier, the H9
isn't limited by hardware controls.  However a slicer, the Harpeggiator
and hard tremolo will only be really effective in a live situation after the H9 is able to
recognize MIDI PLAY CONTINUE and STOP commands.  But I know you guys are
working on that.

Also, a BIT CRUSHER please!  I know
VintageDelay has a very limited bit crush, but something full featured
like a WMD Geiger Counter or a Hexe Bitcrusher.  Controls for sample
frequency (down to 260Hz), bit depth (down to 1 bit), telephone (band pass) filter, LFO for sample
frequency (or assignable) and additional overdrive to really make it nasty.  It would be a real
winner and really set the H9 apart from anything else!