Oh, no I'm serious, there'll be someone somewhere that will pop up to say they put metal down range and the other guy just kept coming/just kept running. It's just the nature of the beast - the post GW II survey on weapons effects found that the bulk of the 5.56 "fail to stop" reports correlated with troops either shooting at distance at hard to hit targets or middle distance shots by troops with fairly basic training in firearms.
In other words, people were far more likely to blame the round/weapon than what might have more likely been a failure to hit.
That's not to say the M4 doesn't have it's shortcomings with rounds developed for longer barrels (excess flash, too low a velocity to make the bullet break up on impact etc) - Abe is perfectly correct (as he almost invariably is!) to point to that factor, which is why a lot of recent development has been put into improving performance from shorter barrel weapons in 5.56.
Of course, for Aghanistan, we could legally just start loading JSP's and have done with it (they're not legally recognised combatant forces...so...meh to the Hague conventions...)
Back on the A2, there's a stack of 'em that are fully loaded with all the add on extras you'd want, we have a much reduced force from the original size of the Army at the height of the cold war - if there's enough of a pool of weapons to permit cost effective reworks on them, I'd see if we can hang on for a bit longer, see if LSAT or something similar takes off. 30% lighter ammo sounds worth it to me.
Other than that, it'd be nice to get a downward ejecting bullpup (FN2000 and perhaps the Tabor fit that description) Home production is no longer an issue because I believe the manufacturing capability went away some time ago, so it'd be MOTS and pick the nicest one. Given the recent advances in materials, something with better resistance to corrosion, lighter and stronger to give a weapon with margins in reserve to tack on the extras the troops have come to expect at a lower all up weight would be useful.