Well. Since 2 years, multiframe editing has been improved.
Nowadays, we can draw additional strokes.
So, all methods to modify frames are supported by multiframe editing.
The problem is still that you have to select all concerned frames before the multiframe editing and don’t forget one.
Ability to add, remove, merge and duplicate GP Layers from dopesheet has been added.
So, in theory, you can use them as instanced frames by animating with their opacity.
Instead of dealing with GP strokes frames for one layer, you are dealing with keyframes for opacity of this layer.
But downside is that you can end-up with too much layers to deal with.
During those 2 years, GP developers redesigned some basics of animation with GP, improved editing of drawing (Curve Editing, Fill tool), SVG Import/Export, PDF export and Non Photorealistic Rendering of 3D objects via LineArt modifier and other new modifiers for GP objects.
But they did not start to mess up with dependency graph to support this kind of 2D animation stuff.