It seems like GPT-4 is going to be coming out soon and, so I've heard, it will be awesome. Now, we don't know anything about its architecture or its size or how it was trained. If it were only trained on text (about 3.2 T tokens) in an optimal manner, then it would be about 2.5X the size of Chinchilla i.e. the size of GPT-3. So to be larger than GPT-3, it would need to be multi-modal, which could present some interesting capabilities.
So it is time to ask that question again: what's the least impressive thing that GPT-4 won't be able to do? State your assumptions to be clear i.e. a text and image generating GPT-4 in the style of X with size Y can't do Z.
Accurately (ie 0% false positive and no more than 10% false negative) idenrify if one paragraph book reviews are plagiarized.
I think even with search capabilities, it wouldn't accurately sort a set of real submissions (eg, if a high school English teacher have the assignment to thier ~150 students - with a note that they would be only mildly punished for plagiarism on this one assignment to ensure at least some actual plagiarized essays in the sample)