most languages wouldn't work properly with ?! as that could be already valid (unary ! operator meaning not, and ? being used for the ternay operator). So you can't distinguish between: foo ?!bar : baz and an interrobang like operator. !? on the otherhand is likely to already be invalid and be parseable as an interrobang since it wouldn't already be valid to have a ? immediately following a ! in many languages. Having both work might be nice, but is likely impracticle for backwards compatibility.