It would be most helpful if EagleFiler supported custom fields, or failing that, at least support the full complement of simple Dublin Core metadata fields (http://dublincore.org/documents/dces/).
Why? In many cases when organizing or locating information, one may be more concerned with the content rather than the properties of the file. For example, I might be looking for a document that describes an event from 1950, though the document itself was created in 2016. In this case, the date created is not useful, but instead if it were possible to populate another field, e.g. “dcDate”, then one could search on that.
Similarly with other concepts such as “coverage” which is typically used to describe geographic coverage relevant to an item (e.g. a document about Warsaw).
The structure of content with DC fields is notoriously variable, so the implementation could just use string fields and leave the consistency up to the user.
Some of the Dublin Core fields are already supported: dc:Creator = From, dc:Description = Notes, dc:Title = Title, dc:Type = Kind.
This all assumes that the fields can be populated of course. In some cases on OS X there are equivalent fields in the Spotlight schema. The worst case would be that these additional fields are present and supported, but only populated by the user (manually or through a script).
For me at least, supporting this functionality would dramatically improve the utility of EagleFiler for general purpose content management.