Well looking below, they are doing just that with Batman: Arkham City and its denizens. To be truly honest, the only character model/textures that look similar from Batman: Arkham Asylum would be that of the titular character. (Batman, for those who don't know what that word means.)

While I do love the new look of Harley Quinn, the generic henchmen and the two new villains shown, I am curious on what is the point now? One of the big gripes from the art department was that detective mode pretty much got rid of all of their hard-worked-on assets. This supposedly was going to bring a change to that mode so that we could appreciate what the art team slaved over, but if you look at the two shots of the "new" detective mode, it seems not to be the case.

There is an even deeper blue tint over everything. Yea, it is nice that there's a bit more detail on the skeletal structure of everyone in Batman's eyes, but again I see myself missing a good portion of the art and visuals due to detective mode being needed or making planning that much easier. I mean, unless the art style they want to convey is that Batman sees everything through blue tinted glass that hides fine details all the time.