I have a standard question I ask (in addition to any other curiosity questions): "what is one thing you like about the company/work environment, and what is one thing that you would change if you could?" After a few people it gives a decent picture of what the down sides are.
What if they prepared with specific questions but you answered them during the interview?
What if a previous interviewer answered their outstanding questions?
Is curiosity about the company the trait you want to optimize for? In other words, does that curiosity translate to job performance?
I also think this question being so open ended and vague will lead you to get a lot of bad/blank answers. What should I be asking questions about?