Currently, to choose an author for a post (or site data export) you choose from a select element dropdown list of users.   This means that, for example, on a site with thousands of users, the dropdown can be unusably long.

For this task, convert the author selection to an autosuggest text field, so that by typing a user name or email in the text element, a list of matching users appears and can be selected from.  Note that this should be degrade for users with no JS available, so that one can still choose an author.