This is possible with FtpWebRequest using EnableSsl property. .NET supports FTP (common) and FTPeS (FTP explicit security over TLS/SSL)
But since ftplib is a wrapper around inetlib.dll, it might need some native work underneath if it's already not supported.
There are 2 variations on FTPS -- explicit and implicit security. explicit is supported, implicit is not. MSDN states that implicit security will be supported in a later version (though the article was about .NET 2 and it's still not supported.)
Since Implicit security is not wide used and is mostly used by linux based servers, I don't think .NET will ever support it.