>I think the only thing that could reinvigorate them would be if some sort of more powerful calibre
Something between a pistol cartridge and a full rifle cartridge? Something like 5.56x45 or 5.45x39 or maybe 7.62x39? We can only hope that some enterprising genius gunsmith will stumble upon this answer and revolutionize the industry with small, light, low-recoil rifles effective at ranges out to 600 meters.