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I think the interrobang is the only one that readers would understand. People already do use the two-character equivalent, "?!".
The rhetorical question mark could possibly be of some use, but readers wouldn't understand it. I don't think it would be of much use, as it's usually pretty clear when a question is rhetorical. And just because a question is rhetorical doesn't mean it shouldn't be answered. A rhetorical question is often used to make a statement, and if that statement is flawed, one way to expose that flaw is to answer the question?
The others, I don't see a lot of use for them, even if people could be taught them.
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