The rhetorical question mark first appeared in the 1580s and was used at the end of a rhetorical question, however it died out of use in the 1600s. It was the reverse of an ordinary question mark, so that instead of the main opening pointing back into the sentence, it opened away from it.
With the increasing use of written text for casual conversation, we've been running up against the edge of what the current set of punctuation marks can express. We've all heard the complaints that "sarcasm doesn't work in text", or that "text can't express tone of voice". Smilies have been developed as a way of simulating facial expressions, a crucial bit of context for casual speech, but I think that expanding the repertoire of punctuation would also help.
I also like the interrobang, although it doesn't really fill a gap the way the rhetorical question mark does. The combination "?!" works just fine, although a case could be made that it looks cartoony and immature, and the interrobang looks more dignified.