Well, I downloaded the example image and (tried) making the hair shapes in synfig. Just making the outlines is rather slow. I didn't make any of the internal regions, but no doubt doing those would be a pain.
I think the "BLine Tool" has much to be desired. Firstly, it cannot create just the BLine. You always end up with some Layer, which does have the BLine inside of it. But when I'm just laying BLines around I would prefer no layers to be created (only exported BLines).
Second, it should allow to create new BLines which include parts of already existing BLines. So once one has all the outlines layed out, it should be much easier to create the required regions by following those already existing BLines.
My idea was to allow to "land" at any point of a BLine (or at any of the vertexes), follow it some amount (or up to the end), then "take off" from it, possibly landing again on another (or the same BLine) or simply following some new user defined vertexes.
Like this it should be much easier to define Regions which are bounded by Outlines. The Outlines and the Regions could follow different arcs of each BLine without any problems. And it would probably be good to have the tool "Connect" all of those BLines for you, so that editting the "source" BLines will adjust everything accordingly avoiding gaps and such.
I'll try coding this sometime (don't get your hopes up, though). Let's hope it's not too
Any suggestions are appreciated also.