Edger is edit-mode tool that “locks vertices on a line” allowing the mesh to behave like it has only one edge on some parts, while that edge is divided. It eases manipulations of mesh that needs edgeloops for subdivision operators.
Modal operator, works with bmesh. Stores edgeloops in vertex groups, makes a list of custom classes that contain each vertex, its two line ends and ratio to one of them. Sets target vert position on the line with stored ratio so when any of ends is moved the vertex moves with them. Deselects all verts from edger groups.
It’s a shame this plugin has some of the technical issues you described, but the concept and current implementation is looking pretty sweet! I’ll probably try this out when not working on time-dependant projects :3