Personally, I'd prefer if they went back to a true "battle rifle" platform. Just like the days of the BAR/M1/M14, get the guys back into the .308 / 30-06 calibers. AR10's/SR25 platforms would give the military better ballistics compared to the 5.56, improved range, and above all increased lethality. Manual of arms would remain the same for the operators, so no cross platform training would be required.
Just as Teichi stated, good marksmanship is hugely important to get bullets in bodies too. I personally hated the ISMT program while in the Marine Corps. It was in no way shape or form an equivalent training tool, when compared to going to the range and actually putting rounds down range. Range time is where Marines are able to improve their shooting ability. ISMT is essentially a big video game, in a big air con'd room. Not nearly as effective as actually running a gun in the field, where temperature/weather/lighting are all dynamic and force the shooter to compensate for the given conditions.