There’s new app for drawing called Feather, it has free version.
Here’s timestamp on YT of how it works. So, basically every first started line is an guide. We can achieve similar effect in GP using 3D Cursor as stroke placement, but only in one plane. This addition of freely drawed guide would be great for Grease Pencil.
You are not limited to a plane. You can draw on surfaces.
That is the same principle. Except that, here, 3D Surface is an infinite surface, created without switching to another object type.
But if you switch to object mode, add a Bezier Curve align to view, enter Edit mode to delete default curve, use Draw tool or Curve Pen tool to draw a custom curve, go back to object mode, extrude the curve, you should obtain a similar surface useable to project your Grease Pencil Strokes on.
In Blender, 3D surface is an object that can be hidden and kept around, if you need to reuse it, later.
It looks like video doesn’t show a way to memorize guiding surface. So, it may not be more efficient than Blender ; if it has to be redrawn, at each iteration of detailing of drawing.
I don’t know if there are addons to automatize that process. But the point of Grease Pencil 3 project, in development, is to create Geometry Nodes for Grease Pencil, that are handling conversion type.
So, maybe, it will be possible to create Node Tools allowing that.
I’m not using the grease pencil so much… but i’m curious… isn’t something like this done by for example the awesome @sophiejantak already two year ago with BLender 2.9 (?) :
