The Firearm Blog has the skinny on a proposed case design that replaces our tried and true brass casing with platic spiral cases. I see a few problems with this design myself beyond the lack of heat transfer mentioned on The Firearm Blog. The biggest issue I have is the fact these cases are almost guaranteed to not be reloadable.
Brass is malleable so after being blown out from the pressures inherit in firearm cartridges they can be resized back down to a specified size. Plastic does not have this advantage and I can’t imagine any plastic being strong enough to survive multiple reloadings. Just chambering and extracting the case will probably damage it beyond repair due to the physics involving plastic slamming against metal. The idea behind the case is that they will extract better but I don’t think extraction is really that big of an issue anymore. Most rifles and pistols have a very low rate of failure these days.