While Canon, Nikon, Panasonic, Fujifilm, Zeiss will have new products displayed at Photokina 2018, it is unlikely Sony will announce any new cameras ahead of the Photokina. Which means we may not see Sony a7S III, a7000/a6700 announced before Photokina 2018.
The official announcement for these new Sony cameras could be ahead of PhotoPlus EXPO in late October. From Sony Rumors:
Sony usually has new camera codes get registered two or three months before official products announcement. While currently there is no new Sony camera codes got registered, so it is unlikely to see new product announced within 1-2 months. Maybe at this year’s PhotoPlus EXPO, we will see a7S III or a7000/a6700 announced. Stay tuned.