Is it possible to unwarp the cylinder (there's no top and bottom faces) to flat rectangular plane in edit mode while keeping the original aspect ratio of all faces ? similar to unwarp the uv but this time, i want to unwarp the geometry itself not the UV. The closest thing is to cut the cylinder into 2 and scale each to 0 and then join them.
Think of it backwards. Use a simple deform modifier and an empty to control it.
Start with a plane, subdivide it and add a simple deform modifier.
Add an empty. Rotate it 90 degrees on the X axis.
Select the plane, set the simple deform modifier to bend, select the empty as the origin axis and set the angle to 360
Then you can just play with the angle on the modifier to do whatever it is that you want to do.