Happened quite a few times to me.

" Your question here, on the other hand, does not ask something that we can go test. You're asking about an algorithm which can be literally anything. " -> the question can be tested.

The 4 downvotes on this question indicate this atmosphere on this meta.

@DavidPostill it's quite easy to check with some experiments. it has nothing to do with opinions.

@fixer1234 I think answering ~"the information is proprietary" is more appropriate.

@fixer1234 the OP typically doesn't know ahead of time if the information is publicly available or proprietary.

@fixer1234 Questions don't have to be a user issue. Many questions posted on this website aren't about problems, e.g. How does a computer restart itself?, which has received 483 upvotes and 3 downvotes so far. –

"because the "answers" you get will be someone's guess, supposition, or opinion (which is not terribly likely to be right) by making inferences based on the outward behavior of the software." -> In many cases, an educated guess can yield the exact answer or a good approximation of it. For example, is for my question the answer is that "BlueJeans analyzes the video to insert the people count", then that's quite easy to verify the answer. No need to access the BlueJeans code.

" few proprietary software vendors do in fact participiate in Q&A on the network, but 99% of the time, asking questions like this is not really productive, because the "answers" you get will be someone's guess" -> there is at least one BlueJeans employee on SU, who already answered one question. Closing the question kills all hope to have an answer, and deter company employees to monitor SU.

Thanks. "But very specific questions about the internals of proprietary software often won't ever be answerable by anyone except an employee of the company that wrote the software." -> the OP typically doesn't know ahead of time if the information is publicly available.

"There's no actual problem to be solved" -> Does a question have to be about a problem? I don't see it specified on superuser.com/help/on-topic. Many questions posted on this website aren't about problems, e.g. How does a computer restart itself?, which has received 483 upvotes and 3 downvotes so far.

"Unclear what you're asking might be a better close reason I suppose" -> Thanks, what's unclear about the question?

@SampoSarrala It doesn't entirely kill accessibility, e.g. you can use OCR, automated captioning, etc. Furthermore, other answers in my example are textual, which shows that if a good answer is image/video-only, then it's possible for other users to post textual answers as complement.

@Ramhound if an answer received 320 upvotes and only 1 downvote on stack overflow, I still expect it to have been mostly upvoted on superuser.

@fixer1234 to me my example proves that we shouldn't have any rule on systematically banning image/video-only answers, just let the users vote.