Have you ever thought on XMP support
PDFE already handles the XMP object, but only for the standard PDF metadata fields.
It seems that XMP is the standard which most archive systems are going to support
This is being said for some time now
IMHO, Adobe made the mistake to choose a too complex , with too many possibilities, and slow to parse, format. But now that MS start to support it, let's see what happens...
In PDF Explorer you are supporting "custom fields" but this is a "running out" model
The custom fields, that are not more than a way to say they are customizable, must continue to exist in the PDFE context.
What I suppose you are looking for is a way to map a PDFE custom field to a XMP namespace/property pair, and I agree that that is something I really need to develop.
Adding all the PDFE custom fields under a specific PDFE namespace schema is fairly simple, but supporting generic property definition schemas is not that easy. I need to take a look to the Adobe XMP toolkit.