The biggest problem, as I see it, is that the Army is looking at replacing the 20" barrelled M-16 AND the 14.5" M-4 with the 12.5" XM-8. Other barrel lengths are available, but are not currently being considered. The conventional 5.56x45 FMJ is very velocity dependent in its wounding mechanism. The immutable laws of physics dictate that no matter how nice or sexy the weapon, a 12.5" barrel is not going to be more lethal than the already problematic 14.5" M-4, and may be less accurate. This would necessitate a better round (not the 6.8 ), a longer barrel, or both.
IMHO, the XM-8 does not provide much value added for the cost. For the amount of money spent, it is my belief that you would find a much better solution to soldiers hitting and killing bad guys in going to the 77 gr. bullet with sufficient quantities for all soldiers to shoot monthly, a good low powered optical sight, new ranges (indoor at BDE/BN level?), and well-qualified marksmanship training at a variety of KD and unknown ranges under varying conditions.
Sadly, politics will most likely overcome necessity.
The SA80 is a POS.
I like the L85A2 as well, and it's much better than the A1. It drinks oil (copious amounts on bearing surfaces), and doesn't fire US rounds very well, though. You have to set the gas parts to extreme fouling to get the rounds to cycle the action reliably.