Allow pre-orders when there's no set availability date
When a product has no set availability date and the product is out of stock, the preorder button is swapped with a message saying "No longer available for pre-ordering". I suggest you make it possible to allow preorders despite there not being a set availability date.
We're especially interested in this for products that are made on demand, so products that we do not have in stock, but which will be produced once an order is made (we cannot legally take payment before we ship).
In 'YITH Pre-Order for WooCommerce' they've solved this issue by simply not disabling preorders when there's no availability date set. I think WooCommerce Pre-Orders should do the same.