@PhilESkyline: The true answer is no. Nolan in an interview said that he was in post production on TDK when Heath died and so the thought never occured to use Joker in the 3rd as he was still working on the TDK. I really apologise for not having a source, it's very late here and I'm not sure what video it is (Might even be a podcast). But I assure you I heard this from Nolan himself.
(Pretty sure this is the interview,)
@kylekrane: As stated above, this is most likely a rumour/joke.