Ah, I have fond memories of Jess Maerterrer’s math plugin. Back before Grasshopper that was my introduction to exploring parametric surfaces in Rhino.
About the mid-surface idea, it is actually a generalisation of the idea of a Voronoi diagram.
If we divide space into regions according to which of a set of point sites is closest, the boundaries of these regions are the familiar Voronoi cells. However, we can also do the same thing where the input sites are not points, but lines in 3d space, in which case the boundaries end up as curved surfaces. Here’s an ancient blog post I wrote about this.