I have a question which is obviously of some interest to people (12 votes, 5 favourites) but so far no useful answers. Is it good form to put it out of it's misery?
If the information there is correct, let it live - other people will benefit from this information even if you personally won't gain anything,
However if the information itself is incorrect or misleading then deletion should be considered to prevent confusion.
Not personally familiar with the topics there so can't express technical opinion.
It may be worth putting a bounty on it if you have the privilege and if it hasn't already been done. It may attract attention from someone who can answer. Even if you don't get an answer I would recommend letting it live. The interest is obviously there and as @jzd said there may be a solution in the future.
If you have a question that is of interest to a lot of people, why would you want to delete it? It's not like the question will be out of date any time soon and the people interested in it will probably still be interested in an answer if it is given much later.
Also there probably aren't that many people that could authoritatively answer the question, so it's not that surprising if none of them showed up after only a week.
And aside of that don't worry too much about it: due to upvotes/answers you couldn't delete the question anyway.
It may be worthwhile considering that it might be a better fit on programmers.se.
It's not a programming problem that needs to be or can be solved today, it's a question asking why something was done in a specific way.
I don't know that you'd get any better a response there though.
Also, if you are very interested, go find out the reason(s) and then answer it yourself. Just because no one else has supplied it to you doesn't mean there isn't an answer, and I'd bet that the people who do know are easy enough to contact. Surely there's a core haskell mailing list.
Stackoverflow is great for getting answers, but it's just as good - if not better - for publishing difficult to obtain information. Do the legwork, and settle it for yourself and everyone else.