Android 6 was released as Fairphone OS 17.04.8 on April 25, 2017.
Android 6 was released as Fairphone Open OS 17.06.4 on June 16, 2017.
Ok, that could have gone better, but in hindsight I cannot see it as overly dramatic.
Anyway … For a while now Fairphone have streamlined the release process so that the Fairphone Open OS OTA updates get rolled out almost simultanously with Fairphone OS OTA updates, just check the last releases.
In fact, since this streamlining the manual installation download page of Fairphone Open OS here “notoriously” gets populated with new versions days earlier than the manual download pages for Fairphone OS here and here.
We’ll just have to see how it goes this time, I guess, but there’s currently no reason to be so pessimistic 
.