I am pretty sure the confession will be saved up for the ending but if Conan confesses only to Ran and no one else the story would have a interesting turn around.
**mini-Spoiler for movie 4 below**
Not sure if anyone noticed this but in the movie "Captured in Her Eyes" after Conan solo defused the bomb with Takagi, Takagi whispered something to Sato which put a shock on her face, probably retold the story. Also when Conan and Takagi was about to be blasted by the bomb Takagi asked Conan "who are you really?"
I'd say Ran is not gonna be the first to find Conan's identity.
