Yesterday PEO Solider had a media roundtable discussion. I should have phoned into the event but I only just realized it was on. One of the topics discussed was the Improved Carbine Competition. According to the PEO Solider twitter account, which was live updated during the roundtable event, the Improved Carbine Competition requirements do not specify a caliber.
Some companies are sure to submit 6.8 SPC chambered carbines; whether they get anywhere is another story altogether.