Illustrator :: How To Easily Hatch Complex Grayscale Image

I've been trying to hatch a complex image with a single pattern, but with different stroke weights.
 
Here I added an image of a simple greyscale image with below the hatching that I'm trying to make. In short: I want to use only 45 deg. hatches in this direction. However, based on the grey value, I'd like the hatches to have different weights.
 
However, since this image is quite simple, only four different weights were needed. However, I'd like to know if there is an easy way to do this for complex images. For this image I just used pattern fills with different stroke weights, but I'd like a smoother and easier solution, preferably one where it would be possible to have many different weights without having to split up the image in thirty different parts and making thirty different pattern fills.
 
I'm not sure if this is possible, but I might be overlooking something. If it would be possible with a plugin, I'd like to know too. Even if there might be a workaround via Photoshop, and the end-result would not be a perfect vector, It'd be fine.