This is something I have been tracking and monitoring closely ever since back in 1973 when I rode my bicycle to audition all the speakers at Radio Shack. Back in those days they were all paper cones, wire, and magnets. Then JBL started using edgewound voice coils and AlNiCo magnets, and the race was on. Nowadays of course we have much more exotic materials, composites, and a lot more sophisticated design criteria.
From my perspective then, and as far as current trends go, I would have to say the one that really stands out is the trend towards higher prices.