Besides general preformens and speed.
My first things come to mind is. This could be “easy” to implement.
1 wb tool needs a automated WB correction.(the colorpicker is not always usable.)
2 keywords which are writeble in xmp.
3 a local adjustment color adjustment more then the one’s we have. HSL with colorpicker?
4 a layer visualisation of selective tone. I would like to see with “m” how much and where the sliders highlight, midtone, shadow and black are of influence.