calibre long predates the epub standard. And incidentally, the epub standard is dead in any case. It's a trivial script to make the change you want to the authors table, using either SQL or the calibre DB API, which is documented in the user manual. For example, to copy author sort to author, something like:
Code:
calibre-debug -c "from calibre.library import db; db = db().new_api; a = db.get_author_data(); n = {aid:v['sort'] for aid, v in a.iteritems()}; db.rename_items('authors', n)"