Google Play analytics for the months of May have been released. Going by the data, the percentage of users on Oreo has grown to 5.7%, nine months after the version of the OS was released. Quite surprisingly, the Nougat user base also saw slight growth.
https://www.notebookcheck.net/5-7-of-Android-users-now-on-Oreo-data-shows.303018.0.html