There are few features I would like to see in Gradient Map editor.
1)Import export gradients by file to improve reusability and interoperation with other tools.Possibly xml or json with or without additional binary format with available file layout.
2)Gradient node offline filters.
Possibly hsl and levels to easely modify gradients without adding other runtime nodes.Better in a post processing non destructive way
(maybe with an additional gradient widget to see the difference).
3)Spline editing mode.An additional way to edit(switchable).May be easier to work on cases requiring non linear gradients with full control over interpolation.
Modes could be RGB,Luminosity and HSL curves.
4) Math function curve generators with fine tuning controls.
Sine, square, triangle, sawtooth and so the ones you can found in sound editing tool.
I found it very usefull as it is hard to make a gradient with many equidistant black and white keys and shift and fine tune them es scale and shift.
this could be put in a different node to expose function editing functionality at runtime and for optimization purpose(special gradient constraints could be exploited to achieve better performances for those special cases instead to follow the standard gradient calculation path using specific math).
4.1) curve mixing (also just like sound editing tools).
5)multiple key selection + scale and shift as just said in the is hard to edit gradients with many keys.Workflow will improve a lot if one could set color on multiple key at the same time or translate them or scale them es by the combo slider/editbox widget.