Having worked with AS drawing and transform tools, I get that a custom control setup may be troublesome on traditional vector layers. I would propose the ability to make a non-rendering "controls" layer, where the shapes that users have made in AS or imported .png files can be set up. Each individual element can be named in the property bar up top like bones, and they will be accessible through the constraints menu for bone setup. They can also be used to create smart bone actions, or have smart bones constrained to them to drive the action. The shapes will have options of driving scale x,y, rotation, and position x,y when a user interacts with the control layer objects to limit or open up what the control object can do for the end user. It would be useful to have a control layer active toggle checkbox to switch between editing mode for creating the custom control art, and active mode for interacting with the controls based upon the properties set up for each object.
I am sure there are things I have left out, and that the list of features requested here is incomplete, but I would be super happy with having the ability to add a user created custom control setup. Maybe this is already possible and I just am too new to the software. Let me know. Posting an image of a rough mockup that I would probably set up, without the mouth controls because it is just more position constraints whose functionality would be similar to other controllers shown.
