ProFTPd: Multiple Domain VirtualHosts on one IP address
Note that with the advent of RFC 7151, FTP now has a HOST command for supporting true name-based virtual hosts, just as the Host header does for HTTP 1.1.
And ProFTPD implements this HOST command as of the 1.3.6rc1 release. To use it, you can either simply use DNS names in your <VirtualHost> section, like so:
<VirtualHost mysite.example.com>
Or you can explicitly alias the virtual servers as needed:
<VirtualHost 1.2.3.4>
ServerAlias mysite1.example.com
ServerAlias ftp.example.com
...
</VirtualHost>
Hope this helps!
Full disclosure: I'm the author of ProFTPD.