Yes, I am aware of PCB to Gcode and the associated GUI.
I actually use FlatCAM, which is very good and allows for double-sided boards, using locating pins.
However, my wish is for KiCAD to offer the option of outputting gCode directly, just like it outputs Gerber files.
I would agree this has a lower priority inside KiCad.
The sort of milling-tooling you seek, often needs quite custom software to convert Gerber outlines to the opposite sense of material-removal.
The rules of material-removal + Drill will vary with machine, which is another reason this software should be more machine-centric.
I have also seen mention of laser engravers used to remove paint, which is then etched, for an outlines-only result (will have isolated copper lands, but they are tolerated)
and then another laser pass, removes the paint on the solder pads.
I’ve not seen a board made this way, but it sounds viable.