Tbh, realisticly looking at it, I think Link is right, many people from the first two films should be back. This is the last and therefore should be a culmination of everything Batman and Gotham have been through. The main focus should be Batman and not a villain this time, he took a serious backseat in TDK and TDKR should be ALL BATMAN, not some silly flavour of the month villain like every other superhero film. Bringing back Scarecrow WOULD work, he's been in the last 2, there's no reason why he won't show up again, breaking out of Arkham, hopefully back on a horse.
But I tell ya who HAS to show. Zsasz. He was in Batman Begins, perfect foreshadowing if you ask me, I don't think Ra's is needed again, since he was just a segway for Bruce to become Batman, but I would be surprised if he shows up near the end for a WTF moment.
In retrospect, Deadshot seems more suitable for the final instalment of a trilogy of say Iron Man. More comic book-ie. I think for this film, the villain should be a mystery right up until the third act, that would really add to the viral marketing that TDK had fun with. Play detective with Batman... shit like that.
But, Batman SHOULD have to kill the villain this time. None of that 'I'm not going to save you' or 'You'll be in a padded cell forever' crap. Yeah sure, he stopped Two-Face by killing him, but Two-face wasn't the main focus and I'm sure they'll come up with some deep, deep, DEEP dialogue between Bruce/Alfred, Batman/Villain, Batman/Gordon to sort that out.
Oh, finally, BRING BACK WAYNE MANOR FFS. GAH.
"The King Stay The King." -D'Angelo Barksdale
Kakeh, you mah boi.