Create an Author Page on Registration

Interesting question, though I have to say it’d be way easier to solve this with a membership plugin – I assume you don’t want that.

I have found this plugin which hasn’t been updated for over 2 years, however the author.php template hasn’t changed much since then. The only way to do this is either querying an author outside of the loop or to capture the 404.php and display the content;

if (!function_exists('show_authors_without_posts')) {

function show_authors_without_posts($template) {
    global $wp_query;
    if( !is_author() && get_query_var('author') && (0 == $wp_query->posts->post) ) {
        // debug
        // echo 'Overwrite default 404 template...';
        return get_author_template();
    }
    return $template;
}

add_filter('404_template', 'show_authors_without_posts');

}

Here’s also an answered question with querying an author archive outside of the loop.