According to a recent rumour from 
Sonyalpharumors, Sony is working on a powerful successor to its XAVC codec that will support resolutions of up to 8K as well as RGB/YCrCb 4:4:4, RAW and Lossless compression.
In contrast to the current XAVC, the new XEVC codec is not based on the H.264 standard but on the newer H.265 (HEVC), more precisely apparently on H.265 Version 2 Profiles and will be used in Sony&s cameras like its predecessor.
The rumor seems extremely likely to us, as Sony would only follow the example of other camera manufacturers like Canon (with the new XF705) and Panasonic who already use H.265 for recording.
Sony XEVC Codec Variants
The obvious advantage of H.265 compared to H.264 codecs is the much higher efficiency: with the same picture quality, videos can be stored up to 50% smaller files. Videos compressed with H.265 require a low bit rate and consume less storage space compared to H.264 - which is especially important for videos with higher resolutions (such as 4K, 6K and 8K).
Like XAVC, XEVC defines different versions for different resolutions, bit rates, bit depths, color samples, and frame rates. XEVC&s capabilities go far beyond those of XAVC: they range from XEVC 2K Proxy with a resolution of 4:2:0 FullHD at 10-bit color depth and a top bit rate of 5 Mbps to XEVC 4K with 12-bit and RGB /YCrCb 4:4:4 with 24fps and XEVC 8K with a resolution of 7.680 x 4,320 pixels, 12-bit, Bayer RAW at 24 fps at a peak bit rate of 240 Mbps (30 MB/s) - a bit rate that current (SD/CF) memory cards can easily support, making it a viable storage medium for XEVC. This bit rate can also be used to record 1080p at 240 fps. Also planned is a XEVC 4K proxy mode with only 24 Mbps and a 12-bit XEVC 2K lossless mode with 24fps at 240 Mbps bitrate.
It is already speculated on the net that the new 8K capable codec could be used for the first time in the Sony Alpha 7S II successor Sony A7S III or an updated version of the Sony FS7. Maybe even together with the new 8K sensor from Sony.
;)