Grease Pencil Material: Animated Brush Tips/Image Hose

With only one brush tip, strokes can feel very mechanical. The viewer can easily see the pattern in the brush texture (similar to a tiled grass texture for a ground), breaking the illusion of reality.

By using a sequence of images for the textures, the brush stroke is more random and natural. The source of the image sequence could be a folder, the layers of an image file, or a spritesheet.

I believe this is possible with Blender's TexturePaint brushes already. Similar features can be found in Krita, TVPaint, and Corel Painter.