I know that Stack Exchange requires questions to be specific, unambiguous, and having single-solution. For example, in the tour page (my emphasis):
Specific issues within each site's area of expertise
Real problems or questions that you've encountered
and, as immediately following,
Don't ask about...
Questions that are primarily opinion-based
Questions with too many possible answers or that would require an extremely long answer
Similarly, it was remarked here that
Stack Exchange encourages specific questions that have a specific, canonical answers."
A quick glance in Area 51 gives me the impression that several proporsals are probably too vague, too broad, or too aesthetics-based to reach attention, though it's just my guess: the literature proposal, the tea proposal, and the ethics proposal, among others.
Of all SE sites, it is generally noticed, say in this discussion, that Stack Overflow has quite strict policy. This is understandable, as SO has gained tremendous popularity, and everyday there are a huge number of junk posts swarming all over into it.
However, certain SE sites seem to maintain looser standard than others. How can an request for suggestion of action in a certain situation in an academy or workplace have a single "right" answer, or how can a worldbuilding, a possible continuation of a fictional situation, be the most likely one among other competitors, as does mathematics or physics?
Is this not double standard? Is the principle of non-opinion-based and allowing specific answers, though well meant, simply ill-defined?
So it seems the rule of each site is decided by adminstrators of their own. Then again, why can't we create literature, ethics, or tea site? I don't understand.