At this point, who isn’t going to be in the Arrowverse crossover event “Crisis on Infinite Earths”? With a huge star-studded cast of DC veterans who have both played heroes and villains, anything is possible.
Considering how Kevin Conroy, the voice of Batman for nearly 30 years, was saying how he wanted Mark Hamill to be in it, it would make sense that the voice of the Joker for nearly 30 years shows up.
Hamill is not new to the Arrowverse either. Originally he played a Flash villain that is similar to the character he is known for, other than Luke Skywalker, named the Trickster.
It would be interesting to see a version of the Joker show up on television, considering how the CW isn’t allowed to have Batman. Do the same rules apply for the Joker? Perhaps this is all a ruse to get media buzz, who knows? We will find out when “Crisis on Infinite Earths” actually launches.