Responsive Interpolation

I would love to see a responsive, live-updating interpolation function added to Grease Pencil, basically identical to that of Flash/Animate's motion tweening.

Currently, the interpolate feature just bakes in breakdowns. That means that if either the start or end frames are modified in any way, the breakdowns are not updated accordingly, and you have to delete all breakdowns and reapply the interpolation.

This is a real hassle, especially when an animation becomes quite advanced, and makes trial-and-error an absolute pain.