Re: The Riddler for the next Batman movie is cast and it's.... (spoil
I had that same idea about The Riddler being involved in the search for Batman since he'd basically gone into exile at the end of the last movie. I imagined The Riddler trying to feed the flames of the citizens thinking of Batman as a fugitive menace, so that The Riddler comes across as a hero (perhaps a detective) trying to bring him down. Then maybe The Riddler's true colours are revealed and once it's clear that his motives are not as noble as they seemed, Batman redeems himself by bringing him down.
I don't know if that plot could sustain the movie alone, so like the last two movies, some other villains might be brought in, as long as they don't overcrowd it (for example, I didn't think "Batman Begins" was too crowded with villains, even though they had Falcone, The Scarecrow, and Ra's Al Ghul all at the same time).
But the only Batman villain I can think of that could be remotely plausible in Nolan's world in the next one (other than The Riddler) is Bane, and even he's rather preposterous with his venom. I think people like The Penguin, Harley Quinn, Poison Ivy, and even Catwoman are just too wacky for Nolan's world. I can't see Nolan even allowing people to call someone "The Riddler" in his movie - it just doesn't work as a believable alias that can be taken seriously like The Joker. I bet if he's in the movie at all, people would just be calling him "Nygma", much like The Scarecrow was always called "Crane".
I guess there has to be a love interest (studio pressure) or at least a major female character, so I'm curious how they could reconcile that without using Catwoman. I wonder if Talia can be brought in for that and maybe tie that back to the first one because of her connection to Ra's Al Ghul.