1) Contrast
2) Sharpen
3) Blur
4) Saturation
5) Hue
to name but a few.
This would open up so many possibilities.
We already have Gamma ect
Also a Glossy node with all the features of a Diffuse node and all the features of a Specular node would be nice too, would save one from having too many Mix nodes in complex shaders.
Hope this makes sense.

Witpapier out