This is probably one of those requests that sounds simpler to implement than they are, but it would be nice to have the option to use a scale of 0 to 1 to move through these. 0 = linear, 1 = exponential. 0 = easing in, 1 = easing out.
This would mean that the in + out option would not be available in this scenario, but that would be possible to math around in implementations. It would also bring about the option to animate the easings which would be fun!
The main purpose of this would be to neat up some nodes with separate curve modes and easings for 2d/3d/4d points which can look a bit excessive at the moment.