Polyester seems to have some interesting advantages, and it's drawbacks don't seem that important on still cameras. I'm curious on how it doesn't seem to have replaced Tri-Acetate on the still film market; obviating maybe 135 with motor winder use.
What would happen if the same thickness and material between the three kinds of finish (135, 120 and sheet) were used? I guess it would be an issue for roll film cameras when it comes down to winding tolerances. But it would maybe make lower scale manufacturing easier (one master roll for everything).