It would happen overnight if combatant commanders demanded it. In peacetime, you have an argument, but if there was a legitimate, coordinated consensus for a "better" rifle from the field, the Army and Congress would be tripping over each other to get it done.
The Marine Corps just recently approved adoption of the M16A4 as standard issue, following a full analysis of requirements and competitive evaluation. Had they wanted an AR10 or SCAR, they could have bought it.
Your preference for a larger caliber is fine, but what works for you as an individual has little to do with what works as a general issue weapon for a large military force.
Even in the hands of trained riflemen, smaller calibers achieve better hits faster than larger calibers.
That's what wins gunfights, assuming the small caliber has adequate terminal performance.
Trading slightly better terminal performance for slower and less accurate has not been the preferred approach since the Sturmgewehr hit the battlefield.
Bull. The Army has blocked any attempt by the other services to upgrade to a 45 ACP, despite the fact that the 9mm has been proven inadequate. This has nothing to do with the effectiveness of the cartridge, it's strictly a logistics and cost decision.
I'm not sure what the logic was of the Marine's selection of the M16A4, but I'm betting a lot of it had to do with the fact that it was based on the logistics of sharing ammo and parts with what was already in the inventory.
The preference for a larger caliber in the desert is not just my personal preference. It's based on after actions reports from firefights that I participated in that were written by US Army officers. In addition, virtually all the special ops troops I worked with carried something other than the M-4. Also, the Marines and SEALS pulled M-14s out of storage.
An M-4 works great for clearing rooms and fighting from a vehicle, but in an open desert fight at long ranges, it lacks the energy to penetrate light armor, body armor, or sand bags. Not my conclusion - the US Army's.
I don't dispute that most people will find it easier to hit targets using a lighter recoiling round. My problem was that in the specific firefights that I participated in, we scored hits at long range and the enemy was still able to leave under his own power. Whether a larger caliber bullet would have changed this is a matter of speculation. All I can say is that in that particular case, which is representative of a lot of the non-urban combat being done in the desert, the 5.56 didn't get the job done.