I would like… .
A proper mod/control matrix like an extra screen that allowed you to assign the 8 knobs to any parameters or groups of parameters on any machine/drum part similar to the control matrix on the AN1X or morph controllers on the Nord Modualr, this would allow you to tweak the elements of the parts you want via any of the 8 knobs during a jam without having to skip through menu pages to get to each part separately.
Kits to be saved with patterns with the ability to mix and match saved user part presets as the patterns are playing. This worked incredibly well on the Polymorph where one save would not only save the sequencer parameters but also all the tweaked sounds in their own A, B, C, D, banks which you could flick though as the sequencer was running, there was also a separate bank to save even more patches. It’s a ball ache having to remember to save kits after you’ve wrote the patterns and I think they’re enough kit memories for each pattern.
A note length feature for the Mono where you would hold down where the note starts then press another step key further along to determine the note length just like on the Future Retro’s, I know you can lock the hold function but it isn’t as fluid to do.
More exotic FX on the MnM as the ones already on aren’t anything that amazing. How about a voccoder, fancy multi tap delay or comb filter/phaser?
An RPS style’ fill in’ sequencer trigger that you could assign pattern parts to the grid keys which would play instantly when pressed, the Roland MC’s and Quasimidi 309 did this very well and it add’s a little live variation to static loops.
A random patch button just to get sounds that you would never normally conceive no matter how useful or useless they are, the Waldorf Pulse gave me hours of abstract fun with this function.
A step hold feature that repeats one step continuously so you can fine tune the locks on that step without having to wait for the step to loop round again, you can kinda do this with the arppegiator in SID mode but it’s not ideal and again worked a treat on the Polymorph.
Different clock divisions for each part if poss?
Oh yeah and a better EQ on the MD as it just hasn't the tonal abilties like the one on the MnM.