Sony is working on XEVC based on H.265 (HEVC) version 2 for 8k
From SonyAddict: Sony is working on a new XEVC codec that includes 12-bit 4k and 12-bit 8k 4:4:4 capabilities. Even 1080p will be getting a boost up to 240fps 10-bit. This H.265 based codec should double image quality. The speculations are that this codec could appear in future Sony cameras with 8k support.