Does the app also work for products that are still upcoming?

I also want to notify customers about my products that are yet to be launched and not just out-of-stock products to give them some kind of a heads up. Can I make the app do that? 

No, unfortunately. The app is specially-designed to notify customers about products that are already existing in your store but went out of stock. What you can do is add the product to your inventory even if it is not yet launched and set the inventory to zero so that the floating button for notification will appear when the customer clicks on the product. However, there will be no distinction that this is a new product that is yet to be launched since the app will detect it as just one of your existing products that ran out of stocks.