The entire idea of a "Top 3" question seems to scream "Idea Generation" and "Too Broad" when first looked at, and if it isn't worded carefully it will almost certainly end up being "too opinionated".
For an extreme example:
What would be the top 3 traits of an "evil" alien species?
There are no constraints in that question to narrow down what we are looking for, and with the way the question is asked it seems like a popularity contest. It wouldn't take long for that question to be closed, though it would be fun for the 3 seconds it lasted.
Instead, what if we asked a more science-based question:
What are the 3 most important engineering rules to take into account when considering the effects of gravity on architecture, (such as when you wish to construct a new house)?
and then constrained the answers, as well as provided a way to grade them
Keep each of your 3 points to a eighty-word maximum (maximum of 240 total) - longer is not always better. Links are encouraged but should add more detailed information rather than containing your answer.
The "best" 3 are those which are capable of covering the most, while also being the most concise and explanatory within the word limit.
Is this still too opinionated? Encompass "Idea Generation"? Too Broad? Do you see improvements that would make it better?
In a more general sense, would it be possible to have well-asked "list" questions if they constrain themselves?
I could see these questions being used for "where to start" on extremely broad worldbuilding topics such as Architecture or Language and I think they would very useful - yet I could also see how, since the topics are so broad, we might prefer that we just don't ask those questions here - and that people go and do their broad research elsewhere.