It seems to me the question is not "how do we define where subjective is too subjective", but rather how do we, as a community, deal with subjective questions in general? People are going to ask overly broad and/or subjective questions all the time on other SE sites. I put those to characteristics together because they seem to be treated the same way and a subjective question is usually overly broad as well.
My casual observations fall onto two conclusions. The first is that subjective/broad questions either flourish with good answers and lots of views and votes, or they are simply ignored. The second is that some sites' admins immediately close them without question, while others let them stand if only out of lack of votes. Either way, my primary concern about subjective questions is that they can be used as reputation farms of sorts, good or bad, which is one of few forms of abuse of the reputation system.
To that end, I would rather see subjective questions regardless of scope be flipped to
community wiki and allowed to follow their own path rather than be closed.