It depends how far these go, and what they imply for the overall design, or how they can be supported by the actual design.
However, I feel that in the past we were quite accomodating in that respect. Again, users may add some comments to this.
The only OS version we can directly support is the one we publish, because that is the one we have fully under control.
Yes.
But to avoid any misunderstanding: a single track can record polyphonic data, in the sense that it can record chords on its steps.
Remember that stacking notes on a step will result in a chord, and not a sequence of separate notes. Now programmatically, a chord is a step that plays its NOTE ON several times at once, but at different pitches. Then, variation can be induced using strum, varying STA, VEL, etc.