I know Robert Henke created Ableton Live and it was a tremendous innovation when it came out.
Over time it gradually expanded features but never dealt with a variety of things that might be development intensive but would in no way break the workflow.
For example:
Support advanced midi stuff. Like, any of it. Why is it so mind bogglingly inconvenient for me to hook up my continuum or my linnstrument to Live?
Loops of arbitrary length/non warped loops, as I mentioned in another comment, are unnecessarily hard to implement.
Why can't I midi map to certain controls, why can't I macro map to certain controls.
Why can't I easily lock stuff in the arrangement view so I am not terrified to change the master tempo.
Why can't I group things in arrangement and edit them together.
why can't I intuitively stretch a sample in arrangement view, when the whole sell of ableton is time stretching?
None of that would break the workflow.