Would it not make sense, therefore, to publish a public cypherpunks mailing list key, which is returned with subscription requests? All incoming message cleartext to the mailing list server would then be encrypted in the server's key; not for security, but precisely for the reason you state above. That _would_ create quite a volume of encrypted communications to each receipient of the list.
Please don't do that. I don't want to go through hoops to read this mailing list. It's already cumbersome as is. Adding PGP in the soup would make things very nasty. I'd rather not use PGP except for private messages. Perhaps having a usenet news group for encoded mail might be better. Something where everyone can occasionally either send a PGP'ed message with the subject being an encoded version of the receipient's name, or with just random junk that's PGP'ed... This would create enough traffic to be able to hide messages in. Perhaps a special "news" reader program can be written that scans all messages in that group for the encoded name, and if it matches that of the reader it will decode it and dump it in that user's mail or read it (and possibly reply to it) on the spot.