Most non-metallic panels that I am familiar with are used on industrial sites where there is corrosive material. Every once in a while some manufacturer will produce small panels for 30A or 60A loads, but they are not service rated. Also these panels present a whole different set of installation problems, such as mounting without warping, cutting holes, and securing conductors and equipment.
From a manufacturing stand point it probably isn't worth the savings to compete against the current standard of metal enclosures. When you consider the cost of approval from UL, NEMA, IEEE and NEC Standards, then tooling for mass production, and convincing the entire electrical industry that they are safe and easier to use. As you can see most of us are against it.
In conclusion, I doubt we will see any panel material changes unless there is a safety, cost, or material shortage which would cause the industry to go another direction.