Samsung’s UK Help centre has confirmed it doesn’t actually know when the final release of Oreo will hit the Galaxy S8:
My guess is that it either genuinely isn’t privy to that kind of information or Samsung don’t have a final date yet.
Is the software ready for the mainstream? No, probably not. Is it a long way off? No definitely not.
I’m still going to guess at Jan/Feb 2018 but we’ll just have to keep an eye out on the updates and will update on Android Addicts when I know more.