According to Shooting Illustrated, a 7.62 x 39 mm barrel and bolt are coming in 2011!
http://www.shootingillustrated.com/4008/bushmaster-acr-2/Bushmaster is not resting on its laurels as the ACR gains momentum. I asked Ryan Smith, Bushmaster’s product manager for LE/tactical firearms, what’s coming down the pike. He explained a new lower-receiver group and magazine will accompany a 7.62×39 mm barrel-and-bolt option in 2011. The company is also determining whether a .30 Rem. AR version will be developed. Contrary to Internet rumors, there is no current plan of action for a 6.5 mm chambering, but work continues on a 6.8 mm SPC version. Finally—and always exciting for long-range nuts like me—Magpul is working on the design for a .308 Win. that may see life as a big brother to the ACR.