I imagine that if if the 6.8 does well i have no doubts that a .308 will follow suit shortly possibly even a few other calibers before too long. It's just too good a marketing tool and an easy accessory for it to go unused. Keep in mind this all hinges on enough people purchasing the chassis and 6.8 kit for it to be economically viable to continue with the line.
There's a thread in the General Firearms section about the RobArm XCR-M that's 308 as well. I'd imagine seeing a 243 Win conversion down the road for it too, and, maybe something based on a 6.5/260 sized bore as well. A little further down the road though, the rifle has to make it to market first.
I have a scar 17 I like it alot but bushmaster could make the acr in a 308 it would be better. I really hope they do. the scar 17 have been pretty hard to get over the last year so im willing to bet there is a big market for the 308