That's a brilliant idea Wingnut.
I think there should be a more mathematical workaround for this. One possible approach may be to get the position of normals. Then we convert them to 2D space by ignoring the Y values. We may be able to use convex hull algorithm to get to outer points. The following links may be good starting points.
However, one delicate issue that is happening here is that essentially I would like to remove all redundant vertices. If you take a look at the playground, the desired result would be that the outer rectangle have only 4 vertices. But now it show them as 8 ( 2 vertices on the left and right edges are redundant as they are on the same path)