I say you all are looking a little to deep into this topic. Re-arming the military is not going to happen soon and new rounds and rifles to shoot them don't grow on trees so were sticking with the 5.45 and the 7.62 NATOs for a good long time to come.
Todays enemies are gorilla fighters, in urban environments, armed with a myriad of weapons and little to no personal armor. That being said, I believe the focus should change from the round to use, to what bullet should be used. As of now, the military uses FMJ rounds, I believe this is the biggest problem with modern rifles.
Anyone who has shot anything with a FMJ .223 round knows how little it is damaged outside of the small hole where the bullet went clean through-and-through. There are 2 very good reasons to change the current ammo to a soft nose or hollow point design:
1) Through-and-through shots in an urban environment are dangerous as hell. You may be shooting at an enemy combatant and using an inhabited house as a backstop thus putting innocent civilians in risk of death. Hollow point or soft nose bullets that can expand in the target help to lower this risk by greatly slowing the round as it expands.
2) Soft point/hollow point rounds are better at stopping a target. Modern wars are fought against radicals whom will happily kill themselves to kill Americans. We should therefore take extra precautions to kill these enemies, not just wound them. Classic wars, such as WWII in Europe were fought by soldiers whom valued life. Upon being shot or injured, these soldiers would stop fighting, being taken away by medics or captured by the enemy. The people we face on the battle field today are different, upon being shot they will blow them selves up to try and kill the friendly soldiers. Care must be taken as these soldiers will fight to the very bloody end and they don't care to live. With this being said, the faster you can KILL an enemy, the less of a chance they have to cause more harm to you. Hollow and soft points do this best as any hunter can tell you.