This script reads the specified file over FTP and outputs it over HTTP. Thus, you can point WP ALL Import at the URL for this script on your server to provide a "bridge" between FTP and HTTP. This is provided with the hope it will be useful but custom PHP and importing over FTP is not officially supported.

import-ftp-proxy.php

<?php
// Note: Anyone could access your data if they guess this URL. You should remove this file from the server 
// after importing or name it to something "unguessable". For even better security use an .htaccess rule.
//
// If you're experiencing problems you can uncomment the following line so errors will be sent to the file.
// ini_set('display_errors', 1); ini_set('display_startup_errors', 1); error_reporting(E_ALL);
//
// Enter the FTP (or HTTP) URL of your data file below.
$url = "ftp://username:password@hostname.com/full/path/to/file.csv";

// These headers aren't strictly needed but can be helpful
header('Content-Type: text/plain');
header('Content-Disposition: attachment; filename="ftp-proxy-data.txt"');
header('Pragma: no-cache');

// Fetch the file and echo it
readfile($url);