Well, according to the latest information Samsung is planning to update their OLD Galaxy S6 and S6 Edge to Android 8.0 Oreo. There's no information regarding the release date or beta program of Android Oreo for the Galaxy S6 Family.
The news came from a redditor who talked to four Samsung executives confirming that the Galaxy S6 will be receiving Official Android 8.0 Oreo Update. "I talked to four Samsung chat reps about whether the S6 will be receiving Oreo. They all said it will, and one of them even told me he talked to his supervisor."
The Galaxy S6 and S6 Edge were launched back in 2015 with Android 5.0 Lollipop and are upgradable to Android 7.0 Nougat as of now.