As for music, a local oldies station here has a saying, "All of the great music has already been recorded." I think there is a lot of truth in that. It's one of the reasons most of today's modern stuff stinks, and is around for 15 minutes or less. There will never be a station that plays stuff from the 90's to 2010 thirty years from now simply because no one will remember it, let alone want to hear it.
I think it's much the same with gun designs. The AR-15 was about the most revolutionary weapon of modern times, and it's over 50 years old. Look at most semi auto pistols. They either are, or closely mimic the 1911. A revolver is a revolver. Not much they can do with it except make it out of something different. They've tried Aluminum, Titanium and plastic. Not much left.
Same with bolt action rifles. Savage, Remington, Browning, Ruger, Mauser, all look and operate much the same. There just isn't a whole lot more to invent. In shotguns they've come out with some new ideas. Benelli's inertia action on the Super Black Eagle is a nice idea that really works well. As for pistols Glock was it, and it was over 25 years ago. Now they're all jumping on the bandwagon. Springfield with the XD, and S&W with the Sigma and M&P. Just a Glock in different clothes.
1911's sell well. That is why everyone and their brother is making them. Just like AR-15's. Yeah, they skeletonize the hammers, checker everything except the inside of the barrel, put on every kind of sight ever manufactured since the dawn of time, but in the end it's another 1911. Some are finished better. Some fit better, and others simply go bang. It's much the same with cartridges. 10 years ago the short fat wonders were all the rage. Now most, like the Remington SAUM's have tanked. People who like guns are for the most part traditionalists.
I think many of the gun manufacturers would be better served bringing out modern replicas of old designs. I'd like to see a NEW Garand with a Stainless Steel gas system, or even a Browning BAR in semi auto produced by a big name like Browning again. The .50 BMG's have caught on well. Gun makers are finding it harder and harder to make a buck today. I think partly because of the "Build 'em cheap, and stack 'em deep" philosophy. Guns used to be handed down. Now many are lucky to last for a few years. As with music, all of the good guns have already been invented. Bill T.