I know this isn't the answer you were looking for, but in the past I've added the "-- " to my .signature. Technically that's not a correct thing to do, but in practice it worked fine for me.
Since I use tin for news, and Mail for mail, this would cause a conflict, since tin automatically adds the "-- " and then appended .signature. As for the deafening silence / technical merit question: I think it's just a matter of priorities. It's not a problem that is stopping anyone from getting work done. Just an inconvenience that seems easily resolved. If I get some time, I'll look into how to add it myself.
