Wait until we get into another Vietnam type jungle war. Our boys will pay the price for all of the emphasis on "high tech" rifles. The enemy will no doubt be using older rifles that were designed to take care of the business at hand.
Hell, in a jungle fight, give me a .45 ACP submachine gun, UMP-45 style, and a LOT of napalm.
In any case, the XM-8 appears very conventional in design, if one simply removes all the electronic geegaws. it's still a gas-operated automatic magazine-fed rifle, just more robust and reliable than its predecessor. Don't forget, polymer won't decay in a wet, humid environment like the M16's aluminum would.