I favor the increased use of plastic materials in auto construction. Where ever the materials make sense use them. Materials Science and Engineering is a steadily evolving art/discipline, and new uses of old materials, as well as new materials altogether are constantly being brought to the marketplace.
The only major downside of plastic materials are their susceptibility to become involved as fuel in any fire events. That may also produce a toxic or at least noxious gas as well. There are ways to mitigate and control that danger, but at some tipping point where most (or at least most of the surface) of the vehicle is plastic that danger may become more serious.
The other trend which I favor is the use of more alloy, esp. Aluminum alloys, in certain parts, e.g. wheels, major & minor castings, engine blocks, Tranny cases, etc.
All of that should add up to a lighter and more efficient vehicle requiring less horsepower to motivate, less braking to halt, and increased duty-life cycle for major subsystems and the vehicle itself. Engines are so much better now than they were, even by the late 1970's, that few people, other than car restorers, even realize how poorly conceived and made all engines from 1900 to the early 1970's really were!
Modern injection sytems, engine management computers, and distributorless ignitions are far superior to all that ever went before. The use of specific alloys at various points inside the engine itself have reduced weight, increased reliability, and made closer tolerances possible. This allows modern engines to produce a great deal more torque and power from smaller displacement engines without having the increased internal stresses reduce engine life. In fact, a well maintained modern engine often lasts more than twice as long, between major breakdowns or overhauls, than any enigne produced in the 50's and 60's. Few people ever own a vehicle long enough, any more, to replace either valves, rings, or bearings. That was not the case for most of automotive history before the past twenty years.
I had seriously thought that by this time we would be siing the use of high-temperature, low brittleness ceramic components inside our engines. I don't know what the current status of the development cycle on those items is, but I recall the prediction that items like that would eventually turn up inside the combustion chambers of engines with positive results.
If you are an automotive engineer invovled all that has happened especially since 1980, feel free to pat yourslef on the back for the thoroughgoing evolution you have put the auto through since you began work.
JB is metajohn@aol.com