We acknowledge the customer demand for Private Channels and have been hard at work on it. Private Channels is currently in preview with a select group of customers. We expect to release the feature to the public later this Fall, and will update here when we are starting to roll out to all customers. We appreciate all the feedback you have provided to us on this forum and thank you for your patience.
~AlexSpence S commented
Microsoft has delayed private channels:
"We'll be gradually rolling this out to customers in late October (previously early September). The roll out will be completed worldwide by the early November (previously end of September)."