Wow, the costume fan art looks great, as does the official art of them in costume. I do think it's a little unfortunate that Oreki didn't get to be a detective as well, but hey, he looks dashing as Lupin. I can't imagine Chitanda or Mayaka as thieves and villains (too nice and too straightforward) so I suppose it's up to the guys. They're all going to have to work on their skills in order to live up to their cosplay.
I regret that none of them are dressed as Miss Marple, the best and brightest out of all the Christie detectives. (Satoshi could have pulled it off!)