iOS 12 is available (as of Monday 17 September)
Today's announcement confirmed 17 September release of iOS 12. https://www.apple.com/ios/ios-12/
So for everyone with paid gigs or critical work, update this weekend to the "final iOS 11" which is I think 11.4.1 and then turn off your auto-updates for iOS. You never know what will go wrong with a new iOS.
For the rest of us, yah I think I'm going for it. I'll be impressed if iOS 12 actually improves performance on my older devices.
[EDIT thread title, now that it is here.]