As the author notes, for such hack to have any chances of working reliably a third party is needed to synchronize connection setup. But a third party with a public IP could also forward an encrypted TCP connection between two machines that do not have public IP addresses. Such approach does not require any hacks and gives a strong guarantee that the third party can not snoop the connection.

The only thing that the third party learns is that there is a connection, but the proposes solution also has this drawback.