imo this would be a very cool feature- a snap point for midi notes.
Permit me to repeat the idea, to hopefully clarify, and make sure I actually understand! 
- we have a number of notes where the start times are different, and we select them.
- Let’s call the earliest ‘x’, and the latest ‘y’.
- we find the difference between y and x, and call it ‘z’, and divide by 2.
- We’ll create a snap point for this group of notes. It is placed ‘s’ samples (the middle point between x and y) from the the earliest note’s start time, on all the notes. (like snap points in the sample editor.)
(y-x)/2=z
x+z=s
When you quantize the chord, the snap point jumps to the grid, and the selected notes come along, keeping their relative time diffs, whether using iQ or just Q.
Sounds like it should take about 5 minutes to program- maybe they can get it into Cubase 9.0! 
