This have been discussed for years, yet the developers are not keen to implement it yet…
The ! _DragMode _ControlPolygon tool is extremely user-unfriendly, so it has little to no real usage. The biggest issue is that it will not limit the sliding of the control point(s) along the control polygon, hence there is a big chance for an accidental movement in a random direction. It does not have the ability to move the control point(s) to the normal direction, too. Not to mention that the user is forced to manually disable the Gumball while working with this particular drag mode, which requires more mouse clicks, including the subsequent enabling of the Gumball.
Having a dedicated ControlPolygonGumball (or Super Gumball) will fully eliminate these disadvantages.