I have asked a similar question here on meta:
were, a mod (Dr. Mayhem) answered:
[...] software recs are on topic, but that some can be, if the question is written well. I think book recommendations should be treated similarly to software recommendations.
[...] but as there is this uncertainty[...]
From what I remember, there have been some well written questions that were allowed, because they simply weren't of the format
suggest me some books for X!
but, they included research etc.
But, generally, these kind of questions get closed, because every user has something different to suggest; thus it is opinion based; thus off topic.
The Chat is a good place to discuss these things.