This would be great - but a challenging mod!
One store I'm involved with works mainly as a wholesaler selling largely via consignment, this brings the other side of consignment into the picture.

The cart works fine for normal retail sales but really falls down trying to track wholesale customer orders and consignment orders, reconciling retail and wholesale is a real pain as I can't find a good way to run them both from the same system and they both pull from the same inventory.

To start of a wishlist, the workflow for could be something like:

1. Sales person (or even the customer) completes shopping cart and selects consignment as a payment option (this should be an option you can set against a customers profile)

2. Against that order as well as their order history, the customer or sales person can print a consignment list report, this would explode each item into a single line in a table with blank columns for "Date Sold", "Invoice Number", "Date Paid" as well as the normal Item Numbers, prices and names. In the simple version they can print this report and use it to track sales in their shop, then email/fax back at the end of the month.

3. In the better version they can tick off each item online as it sells from their account with the store and (typically once a month) move all tick items into a shopping cart to actually pay for them.