Apple’s App Store has a new feature that allows developers to make new iOS 11 apps available for pre-order up to 90 days before release.
Developers can now track the performance of app pre-orders in Sales and Trends. Sales and Trends displays the number of ordered, canceled, and net pre-orders (net represents ordered minus canceled). Once a pre-order is released for download to the customer, it's reflected as a unit. For paid apps, upon successful billing, downloads are released and the associated sales from the pre-order appear.
Before an app is released, users can view the app's product page and order the app in advance. Once it’s released, users will be notified and the app will automatically download to their iPhone or iPad. You'll be charged before downloading for paid apps.