Well it's obviously Nolan North's day for news. In an interview involving North, Troy Baker and John DiMaggio, Nolan was asked which Joker he played by DiMaggio who was then quickly told to shut up.
Here's the exchange which kicks in about 1m10s
Nolan North: Were you just going to ask who I do?
John DiMaggio: Yeah, which Joker did you play in...?
Nolan North: No I didn't.. I did.. We can't... I...
John DiMaggio: Oh. Zip it.
Nolan North: Burn that piece of tape.
He closes the line of questioning down by saying, "I just do the Penguin". What do you think? Unaccredited work in the past or something that's not been announced yet?
Here's the full interview from Outside Xbox which is brilliant. Thanks to James Jarvis for pointing it out.