Often, when an item sells out, customers do not particularly want to be on a "waitlist". Or once an item is in-stock and drops into their cart, they remove it because they don't understand why it was added, or don't want it anymore. This results in lost sales.
I would love the ability to allow Pre-Ordering when an item reaches 0 inventory. (This would not be a specific number, but might need a min/max field to trigger notifications?
And possibly an option "Estimated wait-time"?)
Each Product would need the ability to turn on/off the pre-order option. Then, when an item sells-out, (if the product is enabled for Pre-Order), customers would have the choice of either Pre-ordering and dropping the item into their cart and paying.... or Waitlisting, and being notified when it is in stock. (This option would keep it out of their cart, and it would only drop into their cart when inventory was received, and pre-order (paid) orders were filled. )