Grease Pencil - Animations need to show up in Action Editor

This proposal doesn't need a separate UI; just the ability to save Grease Pencil animations in the Action Editor .

I understand that the functionality for the Dope-Sheet and Action Editor aren't meant to accommodate GPencil's frame-by-frame nature, hence the existence of a separate "Grease Pencil mode" in the Dope-Sheet panel, but I believe creating and saving Actions in the Action Editor could prove useful in the long-run.

For example: Creating complex 2D animations that can only be done frame-by-frame, and then simple rigs with the Action Constraints that allow switching between those animations.

Such a system could potentially help Grease Pencil leap beyond mere Cut-Out animation with deformation rigs and into something that's more of a hybrid of cut-out and traditional animation. It can do so by taking a more modular approach to tradition animation. (I'll even happily create a tutorial for all this.)

It seems that @Joshua Leung (aligorith) initially intended for such a feature back in 2008: blenderartists.org/t/animation-dev-grease-pencil-mode-what-does-it-do/420905/61

Another interesting use-case for such a feature is, of course, with the combination of the NLA Editor, where you could edit the timing of individual Grease Pencil actions and easily change and adapt animations according to animation-direction.