/**
 * Enable unfiltered_html capability for sub-sites Editors and Administrators
 *
 * @param  array  $caps     The user's capabilities.
 * @param  string $cap      Capability name.
 * @param  int    $user_id  The user ID.
 * @return array  $caps     The user's capabilities, with 'unfiltered_html' potentially added.
 */
function wpcninja_add_unfiltered_html_capability_to_sub_sites_editors_and_admins( $caps, $cap, $user_id ) {
    if ( 'unfiltered_html' === $cap && user_can( $user_id, 'editor' ) || 'unfiltered_html' === $cap && user_can( $user_id, 'administrator' ) ) {
        $caps = array( 'unfiltered_html' );
    }
    return $caps;
}
add_filter( 'map_meta_cap', 'wpcninja_add_unfiltered_html_capability_to_sub_sites_editors_and_admins', 1, 3 );