Grasshopper does not seem to have the “pick region” feature from the Rhino Hatch command. I have created such an algorithm, taking advantage of recursive computing provided by the Hoopsnake plugin. You can download the .gh file here: FindRegion.gh
The overall idea of the algorithm is to find the curve that has the shortest angle relative to the previous one. For this to happen, a lot of mid actions need to take place, which are somewhat explained in the definition itself.
If you find bugs, care to contact me!
 In order to avoid using the third-party plugin Hoopsnake, I have devised an alternative approach using SrfSplit. It is much slower, but yelds correct results.