Whether the DOD takes it is irrelevant. They have a boatload of other considerations, one major one being NATO has to go along, too. That makes it a major political/military thumbwrestle to even open up the subject of a caliber change that will affect dozens of governments.
Frankly, it's a little bit pollyanna to think ANY caliber would ever have a chance in that regard.
Add in there are other developing technologies out there, like the LSAT round, which has no brass case at all. It's well into the testing phase, up to and including Battalion level exercises, and SOCOM has signed on as a partner in testing. These guys don't just sit around on a range filled with bench guns. They like using things in actual combat - and have used the 6.8 in A-stan, among others, already. If the promise of half the weight per round, plus the benefit of a twice the ammo per magazine holds out, who even cares about another brass cased cartridge? It's 1860's technology, right? Time to move on.
Suggesting that it takes military approval for a caliber to sell well is ludicrous in the face of the hundreds of others that never were and remain commercial successes. America's #1 deer rifle of the 20th century was the lever action, and it made it's success from the .30-30 - a caliber never accepted by the military. The 6.8 SPC fills the same ballistic role in hunting. It offers good power in a carbine length rifle. It does it the modern way, with a smaller bullet at much higher speeds, from a semi auto rifle that is leaps and bounds ahead of a cranky old black powder age lever gun.
I'm glad it never had a chance to get adopted, the bad mouthing of the 5.56 alone tells me I the 6.8 would have been treated the same - because it wasn't the .308. Fortunately, I don't hold to the One Caliber to Rule Them All, and can make choices that suit what I want to do.
The ACR was just put out for LEO purchase, and you get the choice - 5.56 or 6.8. No, it's far from dead yet.
