It is new, yes: Extension of Shake Animation and Messages. Interestingly they had the つ・っ thing as a shake/warning just like this, but after feedback they removed it entirely. I think your proposal is a nice idea though. Still mark it as wrong, but give the hint immediately. You may want to cross-post this suggestion (or link to this thread) in the topic I linked to above. Keep in mind that some people may not want the answer given to them though, as they may want to try a second time before checking for the correct answer.
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