OK…to make the date column sortable add the following code also in your functions.php file:
function registration_date_column_register_sortable( $columns ) {
$columns['user_registered'] = 'user_registered';
return $columns;
}
add_filter( 'manage_users_sortable_columns', 'registration_date_column_register_sortable' );
Now concerning adding the password column. The password field value on the db cannot be converted into plain text, as wordpress uses a 1 way encryption to store the passwords using a variation of md5 that cannot be reserved. That is why a new password is generated when a previous one is lost. And this is done on purpose so admins can’t have access to their users passwords,as some users are using the same password on different accounts.
However, there are some sites that claims to do MD5 reserve lookup, I think is more of a hacker tool.