New voice for Aku...
Tartakovsky has expressed concern, in the event of a possible film or series revival, with re-casting the voice of Aku. The loss of Iwamatsu Mako was heartbreaking, and there's certainly no one who can play the role in quite the same way that he did.
A more than suitable replacement would be Sab Shimono. He is well known as the voice of Uncle on "The Jackie Chan Adventures," in addition to hundreds of other voice and live-action roles. He also notably played Jack's father in "Samurai Jack," so he's been right under Tartakovsky's nose since the beginning.
Though he usually performs using his normal speaking voice, in his lower register, Shimono sounds almost indistinguishable from the late Mako. (http://www.youtube.com/watch?v=DeHSUs9BfsA)
If there is any chance that Jack's story may see a proper conclusion, the selection of Sab Shimono for Aku should be a no brainer.