I don't think that's what ariich is saying at all. I think he's just baffled by emin saying Two-Face was introduced in the last quarter of the movie. He wasn't. One of the major story arcs thoughout the entire film was his stransformation into 2F. The fact that the transformation didn't happen until the end doesn't somehow equate to him appearing out of nowhere. Significant time was spent from the very beginning developing the story that would enable his transformation.
This. The character is Harvey Dent, who is in the whole film. Just because his character development leads to him becoming Two Face at the end doesn't mean the villain just came out of nowhere.
But yeah, as bosky said, it's doable on the assumption that the League of Shadows is all treated as one story arc rather than going into much detail of the different characters. Nolan did two major, separate villains very well in the first two films, but more than that might get a bit cluttered.
Anyway, it's only a rumour, not confirmed to be true, so let's just wait and see.