If only I ever get an opportunity to write an ending twist of the series, I'd want Ran to be somehow connected to the Black Organisation. Maybe she could be Vermouth's sister, or anything like that. However , things will get resolved in the end , and she'll end of with Shinichi, but this should not be easy. Maybe it will be revealed that Ai Haibara is non another than Vermouth ( LOL) and she has been disguised to take care of her sister ( Ran) and take revenge from Kudo. Maybe Vermouth has some issues with Kudo and she wants him dead, but realizes that Ran truly loves Kudo, so she decides to forgive him ( after a lot of drama, of course)
Maybe Kaito Kid seems to care about Ran because of her resemblance with his girlfriend , who is later revealed to be Vermouth. Maybe Kaito finds out that Vermouth and Ran are sisters and decides to unite them.
Maybe Kaito always steals jewels because the only thing that could lead him to his girlfriend Vermouth ( now disguised as Ai Haibara ) is a ring that she owned. Maybe he sees a same type of ring in Ran's finger and this make him realize that Ran and Vermouth are sisters.
I guess I have already written so much, that is never going to happen though.
I wish..!