I’d like to propose a general purpose onion skinning feature for animated objects/blender viewports.
What is known as ghosting in other 3D packages (I think 3ds max) is already part of Grease Pencil. This is extremely useful for animation, as You see arcs and spacing in screen space. Onion skins are equally useful for 2D and 3D animation, and a much better way to tweak and fine tune animation than fiddling with f-curves
What do You think?