hacky-taxonomy-archives.php

<?php
/*
 * Plugin Name: Hacky Taxonomy Archives
 * Description: Don't use this on a live site, plz. Proof of concept for Aaron Holbrook.
 * Author: Andrew Nacin
 */

add_action( 'template_redirect', function() {
	global $wp_rewrite;
	$taxonomy = 'fruits';
	add_rewrite_rule( 'fruits/?$', 'index.php?taxonomy=fruits', 'top' );
	add_rewrite_rule( 'fruits/' . $wp_rewrite->pagination_base . '/([0-9]{1,})/?$', 'index.php?taxonomy=fruits&paged=$matches[1]', 'top' );
} );

add_action( 'pre_get_posts', function( $query ) {
	if ( ! $query->is_main_query() )
		return;

	if ( $query->get( 'taxonomy' ) == 'fruits' && ! $query->get( 'term' ) ) {
		$query->set( 'tax_query', array(
			array(
				'taxonomy' => 'post_tag',
				'terms' => get_terms( 'post_tag', array( 'fields' => 'ids' ) ),
				'field' => 'term_id',
			)
		) );
	}
} );