After Sony officially announced a7 III (B&H/Adorama/Amazon), next cameras from Sony will most likely be Sony a7S III and Sony a6700. The announcement for Sony a7S III could be around Photokina 2018 in September, and announcement for Sony a6700 maybe in the second half of 2018. Stay tuned for more info.
Famous Photographer Max Yuryev has made a video for high ISO lowlight comparison on Sony a7 III (Amazon/B&H/Adorama) with a7R III (Amazon/B&H/Adorama), a6500 and Panasonic GH5. From the result, we can clearly see that a7 III has best high ISO performance than all other three cameras. It seems that a7 III does have a next-generation sensor.