"List questions" are generally off-topic on stackexchange sites, and SF in particular, because they tend to be open ended, generate debate, have some level of personal preference, and not meet the criteria of being "answerable". But there are plenty of list questions on this site that do have a single, demonstrably correct answer that just happens to be a finite list of items.
Just today, on the front page, there are a bunch of questions with list answers and our treatment of them is very inconsistent:
- Are there any spells that a wizard/witch can cast without a wand in the Harry Potter universe?
- Other than Morgoth, were any of the Valar ever susceptible to physical injury?
- Who are all the characters to have touched The One Ring?
All of those questions have a list-based answer. Some of them are being rapidly downvoted and VTC'd, while the Harry Potter one has 33 upvotes and an accepted answer.
Note that, in every case, we have all of the information needed to build the list, the criteria is objective, and since the works are completed, the list will never change. That addresses almost every complaint people have about list questions.
So, if list-questions are off-topic, where's the line?