They should cast Dave Letterman to voice the talk show host that is clearly based on him! That would be cool. As for future Joker roles for Hamill...I dunno. He seemed pretty clear and definitive about his decision this time. I have a feeling they will cast someone who we haven't heard before as the Dark Knight Returns Joker. Besides which, I don't really hear Mark as that Joker. Not saying he couldn't pull it off and be marvellous as usual, I just feel like the voice would be much different.