Well, in the video, one of the things that senior psychiatrist was saying was that his level of awareness might be better suited to a time at the end of the twentieth century. Might be a clue there. Its possible that by then, Batman's inflexible, rigid idea of justice might be seen as too outdated and outta place, and the Joker's ability to adapt to anything based on the nature of his awareness would prove necessary for turbulence experienced in those times. So an anti-hero of sorts, while Wayne's position starts to diminish or something.

Personally, I'd like to see something where they fight back to back, and actually look out for each other or something.