So, it turns out that “?!” (or “!?”) is actually an attempt to approximate a failed punctuation mark from the late sixties called the “interrobang.” No, really. You can look it up. I did, in my copy of Merriam-Webster’s Collegiate, and found the following: (1967) a punctuation mark designed for use esp. at the end of an exclamatory rhetorical question. The definition includes a reproduction of the actual mark; it’s a question mark superimposed on a stunted exclamation point. It’s as if a typesetter got hold of the matter transporter device from The Fly.
And the moral of this story is, Interrobang = best punctuation-mark name evah!