My problem with the interrobang, besides the fact it's unnecessary ("?!" does just fine, the same way we don't need to replace "th" with "θ"), is that it's so damned ugly and hard to distinguish . The counter [1] -- the open space between the vertical bar and the question mark curve -- is just too cramped ("‽"), so it's aesthetically unbalanced at large sizes, and just looks like a question mark with an accidental sm…
I.e. "there" and "theater" are two different "th"'s.[3]
[1] https://en.wikipedia.org/wiki/Voiced_dental_fricative
[2] https://en.wikipedia.org/wiki/Th_(digraph)#Voiced_fricative_...
[3] English speakers: if you pay attention to how you speak those two words you'll notice that your tongue is doing different things to make those two "th" sounds. This is a weird "archaeo-linguistic" holdover in your "motor-culture". In a certain sense, "you" always knew this but didn't know you knew.