Please let me know if you think balance should be influenced somehow.
For now I played one game with this mod and ... damn, plastic was scarse. I even made coal liquification->cracking->plastic complex on huge coal path, just to produce more plastic. And for the first Factorio game ever in which I had roughly balanced needs for coal/iron/copper. Instead of Iron being significantly more important early game, copper in late game and coal... never.
But I think my problems with oil amounts was in big part, beucause I have not focussed on thinking what recipes are worth it and what are not. Some recipes have favorable ratios, some recipes have bad ratios! (Light density structure is actually more expensive in plastic version). Also, because I lacked oil, I finally used coal in game, so it wasn't that bad.
I personally think it is nice flavour. You shouldn't mindlessly pick plastic recipes always, but if you are low on copper, you have alternative of using 40plastic per each light density structure. I like that some recipes are worse and some are better.
On the other hand, I wonder what do you think on sulphuric acid green circuit production? It is a bit OP, but I made it as such, because I liked idea of technique of circuit processing improving over time. Also processing plates into wires in late game can give you 40% more wires per copper anyway, so I think this (alone) doesn't even affect directly copper ore need for late-game continous production. (because you don't have possibility to obtain 40% productivity bonus on wire-producting assembler, but cost is just 33% lower).
It has big impact on total consumption of resources, as less machines needs less modules, so that might be called OP, but I feel like late game is too slow anyway.
