My experience is based on Desert Storm and I haven't really talked that much to guys over there now. I did see a recent photo taken in Iraq with a Marine with an M-14, so at least some are still using them.
All I can tell you is that based on my experience, I would prefer to carry a larger caliber than the 5.56. We didn't have to carry them for extended periods, so the weight of the ammo and the rifle didn't really make a lot of difference. I'm used to firing 12 guage shotguns and a 30-06, so the recoil on the 7.62 didn't bother me. Also, there's a lot of new technology on recoil reduction that could be applied to a new combat rifle.
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.