Lots of things have been suggested and tested.
Heck, after how many years, they are just in the last 10 really getting lots of the short barreled 'special forces' guns out there, figuring out that they need heavier bullets to keep decent terminal ballistics out of thoseshort barrels beyond 200 yards, and somebody finally realized that soldiers shoot a lot more accurately with a dot or low mag scope than they do with iron sights.
OK, how many of the people here couldn't figure that out? No hands?

If that is reallly where we are, there is a lotof work to do yet.
Obviously, there is a lot of red tape and are a lot of other considerations that come into play when you are considering equipments for hundreds and hundreds of thousands of soldiers.

Something that may be interesting reading...
SCAR weapon:
http://www.defensereview.com/modules.php?name=News&file=article&sid=750

Other thoughts on the 6.8 and such:
http://forums.military.com/eve/forums/a/tpc/f/3101927042/m/322101822