SSH as discard server?

[Brian Candler]

After authentication, the ssh client is almost certainly going to 
request a channel.  If you don't acknowledge that, it will hang. It can 
then request further channels at any point during the connection.  
Handling this requires decrypting the traffic.  Any "sink" server that 
doesn't bother to decrypt packets will need to be written in a way which 
is very specific to the way the client uses SSH.

 From the intro to rfc4254:

    This document describes the SSH Connection Protocol.  It provides
    interactive login sessions, remote execution of commands, forwarded
    TCP/IP connections, and forwarded X11 connections.  **All of these channels are multiplexed into a single encrypted tunnel**.

(my emphasis)