What it should be doing now is bringing the user’s display_name into the name field. If the user’s display name is their email address then that’s what you’ll be getting. I can change the plugin so that it checks to see if either or both the first and last name are set for a user, and if so, use that to fill in the name field.
Edit: the display_name is editable on a user’s WordPress profile page, and Discourse doesn’t require users to supply a full name, so we probably shouldn’t send the full name by default. It can easily be added as an option though.