This demand-testing technique is called a fake door demand test. The idea is that we put the button or menu item into the user experience exactly where we believe it should be. But, when the user clicks that button, rather than taking the user to the new feature, it instead takes the user to a special page that explains that you are studying the possibility of adding this new feature, and you are seeking customers to talk to about this. The page also provides a way for the user to volunteer (by providing their e-mail or phone number, for example).
What's critical for this to be effective is that the users do not have any visible indication that this is a test until after they click that button. The benefit is that we can quickly collect some very helpful data that will allow us to compare the click-through rate on this button with our expectations or with other features. And then we can follow up with customers to get a better understanding of what they would expect.
This tidbit is from the book Inspired by Marty Cagan