IMO, buying new (ie different) firearms for infantry would be nothing short of a waste of money at this, or any immediate, point in time. There are so many better places to put funds than in rifle/carbine development and/or purchase.
Catching up with the Russian and Chinese anti-ship missiles would be a good start, off the top of my head. But also the troops' body armor, the Humvee (and various other vehicles), etc. could all see a degree of engineering improvement, particularly in light of what kind of battle we're fighting.
P Now would be a good time to unveil those gravity-defying alien tech "black blimps" our government supposedly has!)
No, the "rifle" concept, as manifested by the current AR platform, is probably as mature as it needs to be. It's a very, very small component of a soldier's tool belt, especially compared to conflicts like World War I and II. It's still important, yes, but having mobile soldiers (ie lightweight ammo) who don't run out of ammo readily, and an established logistics chain, seem like drastically more important factors to me.