I doubt that the 5.56 M-16 will be going away anytime soon! As someone said, the idea in combat is to throw lots of lead, fast! I would think that in some specialized units, we will see new weapons, but again, in combat the M-16 and 5.56 works! If it ain't broke, don't fix it! Yes, heavier clibers do a better job killing, but with the risk of being un-PC, killing is not always the always best. Wounded soldiers require more man-power and resourses than dead folks do. You also don't need sniper accuracy in field combat, and you can probably carry 3 times the ammo for a 5.56 than you can for an '08 or an Aught-6.
Throughout history, the guys with the fastest weapons are ussually the winners.
Now, for handgun CQC they need to go back to more stopping power of the old .45 ACP.