An industry insider told me that Kel-Tec has a working SU-16 prototype in .300 AAC BLK and they are likely to bring it into production. The first models will likely be the SU-16C and SU-16CA and will cost $50 – $70 more than the current 5.56mm variants.
The first non-AR-15 production firearm to be chambered in .300 BLK was the Remington Seven. This may be the second.