It would be nice to expand on Bug 7131 by providing an option to delete all 'on order' items on a bib when importing. This would allow for 'overlaying' of order items with full item records when it is not possible to assign either a matching barcode or a matching item number in the file being imported. This could be done by checking the Not-For-Loan value: if it is -1 then the item is an on-order item and can safely be removed. This would obviously not suit all library workflows and could be dangerous for some, so would need to be either a syspref or an option to select during import, or both. Admins or librarians could choose whether to always delete items with NFL = -1, or only do so if they also do not have a barcode.
Bug 24307 has a very similar idea/use case.