Thanks for the post, I understand what you mean, but in my case "nearly flat" isn't good enough and in the end, they're not- converted to triangles (necessarily).
I model papercraft models and the pieces I want to unfold should always be flat n-gons if possible.
Sorry for the shitty pic, I drew it on my phone.
The upper model is a cube that made of flat quads. It unfolds as squares, because the geometry doesn't need triangulation in the end.
In the lower model, I moved a vertex a tiny unit along the top quad's axis outwards, and immediately the front quad is no longer a "true" flat quad because it HAS to be triangulated.
This is a simple example though and it's easily fixable with the method I showed in the Original Post, but what I'm after is something that works with all nonflat quads in the model simultaneously. And if possible, n-gons too.
I'm not sure but maybe the words I'm looking for are "automated, exhaustive scaling of Y to 0% of each n-gon along their normal directions."