On September 13th at IBC 2019, Sony will have a live stream event for new product announcement. According to latest rumors on the web, Sony could finally announce the new a7S III full frame mirrorless camera at IBC 2019. The Sony a7SII was announced at IBC 2015.
Sony currently has one new camera code WW942051 got registered, this camera code has same 5.8GHz Wi-Fi as Sony a7R IV. So this will be a high-end E-mount camera (a7S III or a9 II).