I posted this suggestion in the main thread but since this one is dedicated to Freeze, here it is.
For me, this character would work better as a secondary one. With his quality arguably tied to his tragic origin story, he could play a role similar to Dent in TDK. That good guy whose we are witnessing the downfall, more or less caused by the main plot. He would then end up being some sort of a wild card in the last third of the film, a final “surprise” punch after the expected climax, revealing even more to Bruce how his actions and choices are affecting the world around him.
Let's imagine that in the next movie Bruce puts behind him his blind revenge for a larger approach to justice. He could try to do more as a public figure and, per example, meet with other Gotham high society members for a city revitalization project. Victor Fries could be featured here as a promising scientist. We could get a little glimpse of his research and how everything he do is guided by the hope of saving his wife from whatever her illness is.
Later in the movie, without specifically using the Court of Owls, let's just imagine Bruce being targeted in an attack to keep him from trying to clean the city. Fries could be a collateral victim and lose everything on this occasion.
Then, for the last act, interpreting this incident as proof that corruption and mafia methods are still present, "Freeze" now born would embark on a short killing spree against those Gotham high profile figures whom little games caused his loss.
He could even target Bruce Wayne, and why not showing up at the Manor in what would be the very last scene. There might be something very strong about watching Bruce, without his vigilante costume, encounter a collateral victim of his crusade, cursing his name. His parents name. If Reeves chooses to build his story around themes like family or legacy, there might be some interesting scenes to create here. At least in my opinion.
