As more and more DX Clusters are moving toward user authentication b4 Spot submissions are allowed it would make sense to implement native SSH support to connect to internet DXClusters. It's not the best practice to use cleartext Telnet to transfer usernames and passwords across the Internet in general. Using Telnet is like sending a Postcard with your username and password on it, everybody can read it along the path.
B4 you ask yes there are DXClusters providing ssh access already.
Secure Cluster connection
Secure Cluster connection
Flex 6600 - Spiderbeam