I don't mean to hash and rehash this subject over and over, but I think that my understanding has developed to the point where I believe I can offer something somewhat concrete.
Over the course of this site, we've struggled a bit with how much doctrine we should allow and what types of doctrinal questions should be on- or off-topic. I think that a comment to the latest round of specific questions on this subject has opened my eyes and help me gain some clarity on this subject.
So, I'd like to propose this new guideline for questions:
Questions are on topic if they are focused on the text, rather than things to which the text may apply.
Questions that seem to be seeking to apply the Bible are off-topic.
On Topic: What does "living sacrifice" mean in Romans 12:1
Off Topic: What does it look like to be a "living sacrifice" as Romans 12:1 mentions?
On Topic: Does Hebrews 6:4-6 imply that we can lose our salvation?
Off Topic: Should we accept Hebrews 6:4-6 as an argument for possible loss of salvation?
On Topic: Why are some birds listed in Leviticus 11 and others not?
Off Topic: Is Leviticus 11 useful for birds not known at the time of authorship?
On Topic: Did Paul disapprove of baptism of the dead in 1 Corinthians?
Off Topic: Is Paul in 1 Corinthians saying that baptism of the dead is wrong?
I tried to make the distinctions as subtle as possible there but still accurate to the above guideline. That last example is particularly subtle until you have this Wikipedia article in mind.
The essence is this: Is the OP attempting to understand the Bible or apply the Bible? Application of the Bible is obviously doctrine, which we all agree is off-topic for this site.
What do you think?
Is this a good guideline?
The biggest challenge of this is that we are attempting to get into the mind of the OP. That's what makes this a guideline (since it's subjective) rather than a rule.