Hole Tool: Countersunk, Counterbore or Simple holes

Proposed operation (3D groups):

A new sketch tool would be added. Once selected and the mouse hovers over a plane face, that face is highlighted as usual. When left mouse click, a hole entity is created in the 3D sketch group AND the solid model is modified. Multiple holes could be created in a single group.

The sketch entity might be a circle with cross-hairs and a center point. The point would be constrained to the face clicked on and the normal for that face would be used to orient the entity and hole. The point could then be dragged or constrained as usual.

implementation

One key issue is how to define a hole. Using 2 diameters, a depth (of the counterbore), and a checkbox (counterbore, countersink, normal) would cover the basics. Some people prefer to specify a countersink by the angle as on the wikipedia page. I assume the definition will be in the text window. It's not clear to me how to define the final depth - should it be parametric (per hole) like a normal extruded hole, or defined in the text window? What about non-through holes?

If the depth is draggable/constrainable, an additional line or circle may be needed but will these will all need to be part of the single hole entity. Also, how would that work with the 2D option below?

Once a hole has been created, its definition should be used for subsequent holes until one is edited. It might also be possible to copy/paste a hole entity, which would bring along its parameters but take its normal from the new location.

2D option

People will probably want to use the new sketch entity for 2D drawings. and of course they will want those holes to be formed if they extrude the sketch. The 3D option is more universal but not as nice for simple designs mostly covered by a 2D drawing, so this seems important. Biggest issue is that the 3D NURBS behavior would be quite different between the two. Hole would be created from previous 2D sketch entities AND current 3D group entites, both after the solid model is created. Maybe that's not so bad.

Hole styles?

Would it be feasible to allow the user to create named hole definitions, similar to line styles? Would the hole style be shown on the sketch?

Key questions:

1. what is the best way to define a hole profile?
2. how to handle the final depth of the hole?
3. are there any other important types of holes to handle?
4. is this too much violation of the SolveSpace group structure?