The latest developer beta of iOS 11 is out, and in an interesting twist, the Messages in iCloud feature (that syncs all of your messages on every device into a single backed-up store via iCloud) has been removed:
The “Messages in iCloud” feature has been removed in iOS 11 beta 5 and will ship in a future software update to iOS 11. Users can continue to receive and store messages on each device, and they can continue to backup and restore messages using iCloud Backup.
That wording suggests this feature won’t ship with iOS 11.0, but a subsequent update. It suggests that the feature’s not quite stable enough for Apple to migrate all iOS users to it just yet, and so it’s being removed as the company moves closer to shipping iOS 11. (Presumably we’re six or seven weeks away?) But the feature’s not gone—presumably an update in October or November will turn it on, after Apple’s had more time to perfect it.