[qrv3w]

That's a great idea! I think you're absolutely right - in the video of the plotter I used a pen that has a more flexible nib and pressing it down (especially at an angle) will add more line weight. I'll have to encode the line width along the line now :)

[woolion]

There is a Posca with a brush tip and good ink flow. The easiest to find is the Pentel, but does not flow that fast so you'd have to adjust the speed. So it might not be that easy, and require some experimentation...