Are hypothetical questions that are limited to a specific scenario valid for asking, even though the chances of the scenario actually occurring are very slim?
The FAQ, elaborated here, says "questions about Jewish practice" are in-scope. I believe that means that the question must relate to the Jewish aspects of a practice, real or imagined. There are certainly non-deleted questions having to do with extremely specific and infrequent scenarios already on the site (example).
Elsewhere on meta, the guiding principle of stating the motivation for your question is recommended, as it helps give useful and informative answers. I would think it worthwhile to apply it in cases such as these to determine the goodness of a question. "I imagined this scenario" would not independently constitute a justifiable motivation, but "I imagined this scenario and expect that myself and people I know will one day occupy it" would.
(This was influenced partly by the discussion recently linked in Chat about efficient sock pairing on meta.SO.)