The most likely reason this rifle is not offered in 6.8 SPC is that it's being marketed squarely to the law enforcement community, which so far, has shown zero interest in this cartridge.
The impetus behind the 6.8 SPC was the development of a cartridge that would provide more downrange energy than the 5.56 mm, but still function in the A-2/ M-4 platform. This came at the request of special forces units who were dissatisfied with the performance of the 5.56 while engaging targets at long distance (400-500 meters) in Afghanistan.
Military & law enforcement needs are often quite different, due to the nature of the environments each operates in, which accounts for the lack of cross-over for the 6.8 SPC.
If that weren't enough, the law enforcement community as a whole is slow to embrace new ideas, which would even further slow the acceptance of this new round. A perfect example of this is the resistance of departments to transition from the ol' six shooters to auto pistols in the 1980's, despite most of the criminal element already possessing such weapons & outgunning the police at that time.
The sporting community (hunters) also showed an early interest in this cartridge, but again, the 7615P was not designed as a hunting rifle.
