The request is to add an eye dropper tool to the curves and HSL tool, which allows the following:
With the eye dropper active the user can move the cursor into the image to the location he wants to adapt. There the left mouse button is pressed and the mouse is moved up or down to increase or decrease the curve for the clicked area.
In Lightroom this is called ‘Target adjustment tool’ which can be seen in action here :
Note: This is not a local adjustment. It is not a new global adjustment. It makes just the curves and HSL tools more intuitive.