SKULabs enables you to identify and easily find backorders for products that have gone out of stock.
Sorting orders by Fulfillable Status
You can view backorders by sorting the Processing table on the Orders page by the Fulfillable status column. Start by making sure you have the Fulfillable column enabled.
After that, click on the Fulfillable column header to sort the table.
To filter out unfulfillable and/or partially fulfillable orders, simply uncheck those options in the Filter menu:
Another option is to tag orders that are backordered so you can filter by tag. This is especially handy if you want to quickly show ONLY the orders waiting on backordered items: