+1 for the granular. This would definitely make the H9 stand out.
Programmable filter with lfo, notch, low & high pass, resonance and the sort. Being able to set these parameters to sweep independently would also be awesome for synth.
Dedicated tremolo with programmable rythm-effects
and +1 for different tunings
Tripple delay with sync and option for running the delays in parrallel or seriel
+1 for access to more (hidden) parameters [Perhaps a dedicated midi hardware controller could be an interesting addon]
