Surprise, surprise. If things remain as they are, Windows 10 users who upgrade to the Anniversary Update won't be able to turn off Cortana anymore using the Cortana settings.
If you compare the start menu settings of Cortana of the current version of Windows (version 1511) with those of the Anniversary Update (version 1607) you will notice that Cortana's off switch is no longer available (thanks Ian Paul @ PC World for spotting that)
Microsoft made an interesting decision with Windows 10’s Anniversary Update, which is now in its final stages of development before it rolls out on August 2.
Cortana, the personal digital assistant that replaced Windows 10’s search function and taps into Bing’s servers to answer your queries with contextual awareness, no longer has an off switch.