Make it a project option to write the username of the person who last edited an element, along with a timestamp to a parameter on the element. The parameter can be called "Last Edited by". I work on a big project with very many people involved, and some rotation with people leaving and starting in the project. We have created a parameter for this purpose ourselves, but since it has to be filled in manually, it is never 100% reliable. Perhaps Revit can just fill it in automatically? Or to be more accurate, just don't remove it when an element is relinquished, because it is already displayed in the element properties if it is currently being edited by someone.