The fundamental problem is determining when a question is hypothetical rather than practical. The first two, for example, are unlikely to occur for the vast majority of people on Earth, but they could apply to very particular circumstances for very particular people; I feel that such questions should be given the benefit of the doubt and answered seriously. One thing the Stack Exchange model excels at is providing a lot of experts for answering exactly this type of niche problem.
The third example would easily fall under the new close reason "Primarily opinion based". It's about a situation that, as far as we know, never happened, nor is likely to happen in the forseeable future. Answers to such a question would just be rife with speculation, which is not useful.
It could, however, still be a legitimate concern for (for example) a professional da'ii who also happens to be working for SETI. Unlikely, but possible.
Given the difficulty in judging "hypothetical" vs "practical", I don't think a blanket policy would be a good idea. Rather, such questions should be judged on a case-by-case basis; if the questioner doesn't make a strong enough case as to the question actually being useful (whether it's practical or not), then downvoting should be sufficient.