Hi Max, for the tapered outlines using curve-to-curve Flow could probably work.

If you make a line 1 unit long, and then interpolated curves made with 3 points, with ends at the end of the line and the middle point at x=0.5, y = thickness , that could then work for Flow onto the long bendy curve, with the "Stretch" option enabled for Flow so it goes along the entire length of the bendy curve instead of only 1 unit along it.

Line setup would look like this:




That's with a one unit line, then an interpolated curve above and below it. Then a Flow with the line as the base curve and a bendy curve as the target curve, with Stretch enabled should give this:




- Michael