I don’t know if this is possible/practical to code, but I have an idea:
Subdivide a plane once, giving you 4 inner edges in a + shape. Say you select one of the vertices and set it to passive. When you lift a corner on that side, the passive edge goes with as though it isn’t there, as though the plane wasn’t subdivided. In other words, the vertice didn’t act as the end point for deformation, the other corner is.
This would be helpful in rigging, where you want stretching between two points, without fussing with constraints. This idea came up when I was thinking about rigging the pectoral muscle to the upper-arm. You want a straight line maintained, but it’s tricky with subdivisions.
If this already exists, let me know. I’m not a heavy Blender user (no time).