I like that, it's a good question. Nobody's actually asked me that, which is odd because one question I like to ask all candidates I interview is the inverse ("If you could change one thing about $our_product, etc"). You'd think somebody would have flipped it around on me!

Would you expect an honest answer to that one?

It usually throws the interviewer off, sometimes they need to take a long time to answer, which can be good or bad, but its up to you to decide how honest they're really being