I'd just want to mention something that I thought of. Depending on how complete your ONIX metadata is (the form for the publication format in the catalog entry modal), it is possible to configure a set of publication dates associated with each publication format. ONIX can be pretty thorough, and includes things like 'date first available', or 'embargo date', and so on. These dates are independent of anything set by OMP when publications are actually marked as published during the submission process. Right now, we don't offer this, but it might be possible to have a press setting that allowed editors to use ONIX dates for sorting if they are available, and then fall back to regular publication dates if they are not.
This would add a bit of complexity to the SQL for retrieving monographs, and may cause confusion if someone isn't aware of how much ONIX data has been entered for a publication format, so I'm cautious about implementing this, but figured I'd put it out there.