I'm wondering if there's potential for the new engraving tools to be automated somewhat...
First make "lines" in a region covering the area where you want to place the engraving.
Not really lines, but closed path polygons like those the calligraphy tool makes, but they could be generated from strokes or made with the new engraving tool that guides the calligraphy tool relative to another path, either way.
At this point the lines are of uniform width, so there's no 'image' in the engraving, it's just a patch of lines.
Then apply the thinning / thickening tool to the patch of lines to form the image... here's the automation part. Instead of using the thinning / thickening tool by hand, apply it in a grid of points covering the path of lines the same way the tile clone tool can 'trace' a characteristic of the clones over an underlying image.
I.e. thinning or thickening occurs at each point in some grid of points based on the amount of black in an underlying image. The thinning or thickening being applied to the patch of lines you've created.
I hope this makes sense, I think it's a fairly simple idea - if not let me know and I'll draw it :-)
Cheers -Terry