If the Army is going to make infantry drag around a full size rifle it might as well give them a cartridge of at least .308.
If the Army is going to send everybody who rides around in vehicles into battle with weapon with modest range and knock down power, they might as well make it short and handy and shoot .45 or 9mm. I saw a photo from this year of a Special Forces vehicle manned by soldiers armed with Sterlings. These are basically upgraded Stens, in 9mm, issued by the Brits in the 1950s to eveybody who didn't get a full size rifle.
What ever new weapons that are adopted need to be at least as rugged the AK-47.