In the BibLatex manual there are a number of special fields listed in Section 2.2.3 which we currently do not have support for. It would be nice to have that. I think an extra tab "Special fields" (which is maybe not the best name considering that we have our own special fields... "BibLatex special fields"?) would be an easy solution and add a new class of fields to each entry type?

There will be a duplication of some fields, e.g., keywords and crossref but maybe that is OK?