Wow, you posted this idea in 2014, and in 2020 still not available. Next to the "Allow Back Orders" drop-down, if "Allow, but notify customers" selected, should be a couple of fields to enter the estimated back-in-stock date and quantity. Then, when that date comes should switch to in stock with the correct quantity. This is a brilliant idea and WooCommerce mush have included this feature by now...
Wow, you posted this idea in 2014, and in 2020 still not available. Next to the "Allow Back Orders" drop-down, if "Allow, but notify customers" selected, should be a couple of fields to enter the estimated back-in-stock date and quantity. Then, when that date comes should switch to in stock with the correct quantity. This is a brilliant idea and WooCommerce mush have included this feature by now...