When I am making new filters, I often think that a second external source would come in very handy.
Not only 2 photographs, but for example black and white line drawings of a black curl on a white background or an other shape.
Imagine what you can do with 2 different image components, with 2 image inputs in perlin noise, gradient and it would be great for pattern making, fabrics and layered laces.
And you can blend to your hearts content.
That way you can work more figurative instead of abstract.
Or a photograph in the noise distortion source and a black and white image in the distortion parameter.
Offcourse I have no idea if this technological even can be implemented and
if it actually can be, that the rendertimes will go through the roof like the hdri import times.
But I can imagine the possibilities.
May The Forge Be With You