polymers, not so much, beyond the gutta percha, and rubber grips used over 100 years ago, however "modern" polymer frames are now well over 50 years old, the Nylon 66 Rifle being over 60.
Night sights are approaching that, if not passed it already.
Fiber optics that actually work are not, but are around 40 years old now, at least.
but I don't the poster was talking about the largely irrelevant material upgrades. It may be plastic but its still the browning tilting barrel, or blowback for 99% of whats out there. Even the more exotic designs can be tied to 80 year old designs in most cases.
Ultimately, we have not progressed technology to make anything stronger than we did 100 years ago, only cheaper, or lighter. Because of this, designs cant be much more efficient than what we already use. Its unlikely they ever will. We will probably have Phasers before a working caseless rifle.
Ultimately, there is no motivation for change. The patents are gone, and browning camming barrel designs allow accuracy and durability well beyond what virtually any human can take advantage of, at a price point that cant be beat by an innovation based product.