One of the first things i would request is microtonal scaling /quantising on midi / cv's and if its not there already the ability to use tracks just as modulators and possibly as modulators of other tracks parameters ( to shift signatures per sequence / track , alter start and end points of tracks and transposition etc .
Maybe some way to allow non quantised cv would be a good start .
As some feedback for development i worked with the Notron a Notron for years , the Octopus also and the Circlon and the Zyklus and they each have unique features.
Zyklus - midi note triggered sequencers , midi note on plays sequence , note off stops sequence so you can play / transpose sequences by play them , we kind of have this now with Modals take on step sequencers.
For your sequencer a way to trigger the sequencer to start and stop using midi note on and off midi messages would be great so the sequencer plays whilst the note is held and stops when the note is releases .
This allows the sequencer to become an amazing phrase player of a kind .
Octopus - deep.....very good for create sequences that keep evolving with controller tracks that alter other tracks , it also has custom directions and other tricks .
Notron - its genius was really the supersteps ( lfo waveforms per step that allow the user to alter midi cc / parameters , great for trills , odd pitch mods per step , just unique stuff , the world needs a sequencer that has 30 or so custom lfo wave forms that can act as modulators on steps , one of the funkiest things you will hear.
Regards this your essentially looking at a deeper level of per step modulators where each step could have a different lfo waveform on it , this can be very interesting also for tracks where a sequence is one sustained note and the modifiers on each step continue to modulate that sustained sound.
That reminds me that the ability to place modulators / midi cc on a step without a note trigger is essential
I am wondering if the sequencer already allows a sequence to only contain modulation data / midi cc's and using different sequence length modulate the note data in polyrhythmic ways.
Notron has one other trick , it could alter sequence / track position with an encoder so you could basically keep shifting one sequence relative to others in real time and also momentarily freeze a track if you were clever with the encoder , great for sequencers that are playing along and then machine gun repeat and then when you let go of the encoder it releases the sequence.
Cirklon - just really good for always evolving stuff and also timing like nothing else and also just a quality device but it could have more of the above