just a few lines, to give you an impression of the next step for LabCurves (16 bit L*a*b* curves for GIMP).
Since a link to LabCurves is always followed by a link to L*a*b* color space basics, people seem to have troubles with this color model. Although it is very powerful for image enhancements it is rather unintuitive. Working with the luminance L* is still ok, but working with a* and b* seems more or less try and error.
So, here is an approach towards usability with L*a*b*: a saturation curve which will work relative to the luminance or relative to the hue. I hope this will be easier to handle than a* and b*. And since harsher saturation adjustments are prone to banding anyway, they will profit from the 16 bit in LabCurves.
It is still work in progress, so you still have to wait a few days... The image edited in the screenshots is a 8-bit jpeg, after some minor luminance adjustments you can see the effect of the saturation curve; one image plain, one image with adaptive saturation and one with absolute saturation applied. The x-axis corresponds to the hue (which is not yet reflected in the GUI), starting with red on the left side.
Enjoy your weekend,
EDIT: Added a newer screenshot.