Whether Warner Bros ultimately decide to reboot the Batman universe (as is supposedly their intention), or to continue the Nolan thread with a different director, and possibly without Bruce Wayne (at least to begin with), they need a tent-pole addition to the cast or story to herald the arrival of a new Batman era. Christopher Nolan had no such problem - his reboot came as a response to a franchise that had lost its way, and whose last film was little more than a bloated joke that threatened to destroy the credentials of the character and made Batman an almost poisoned property. But Nolan came to the rescue, fixing the character and reinstalling him as a screen legend after the flippant over-theatricalities of Schumacher's Batman & Robin, and though his final film was not universally loved by any means, he has vacated the director's chair with the perception of the character at an all-time high. There is no need to wipe the slate and start again, so whoever brings the character to screen next has to get over the fact that they are rebooting (or continuing) a character who will still have inflated expectations attached. The only answer to this is a huge event, and there is none bigger than having Batman and the Joker face off again - that is arguably the most fan-friendly solution of how to get the fans on side straight away.