From my understanding, eggdrop is gearing up for this in the re-write that is slowly taking place.
The socket code has had a major overhaul, which makes it a lot simpler and more expandable.
SSL may well be one of the plug-ins available on the expantion side.
Others will include socks4, socks5, http and other proxy support, using a simple plugin.
However, do not expect this for a very long time. Changes are taking place slowly, with care in creating good strong and stable code. Most items have not even been thought out to completion, so parts can't even be coded.
1.6 series will not see this support (most likely)
The way an ssh tunnel works is you set up one endpoint on your computer (usually) and another to the destination (the irc server). Then you connect normally to the local endpoint and it gets automatically encrypted and tunneled to the remote endpoint. There is no modification needed to eggdrop, as far as I know, since the tunnel is an external resource. Just connect your eggdrop to the tunnel as if it were an irc server, e.g. .jump 127.0.0.1 1234 (or whatever port you use)