So what are the hidden features? The article doesn't say and I scrolled through all the comments and nothing popped out at me other than a bunch of comments of people bashing windows and sucking their own dicks over Linux?
The hidden features are flags that Microsoft enables or disables for random users as part of A/B testing. The article contains a link to the various flags that can be enabled depending on your edition and version of Windows.
Afaik it's a tool to interact with an API to override A/B testing in an official way.
Apparantly some tool already exists that does it. Just not the official way.