If they want to do some stunt casting, if James Avery has any role, they should get Alfonso Roberio to guest voice, he has done voice over work on Robot Chicken. Or maybe he could even be Baxter. I am sure he can play serious.
Anyway I do hope it is somewhat faithful to the Mirage Comics, but have some originality of their own. Using things from the comics, and all other media that they like and some original ideas would be great. What I would like to see:
April should be a scientist or at least have a sciensist mind, she was Baxter's apprentice.
Another thing, I would love to see Shadow in this series. Though they would have to change her background story being this is Nickelodeon. Born out of wedlock whose mother died giving birth to her, that wouldn't fly on Nickelodeon. She was a baby in the original comics, and a teenager in the time skip volume 4 series. If she was a baby it would get boring quick, and a teenager would be an improvement, but I don't know. I would have her age be a pre teen. She would be some homeless street hustle that Raphel and Casey meet on the street,, than Casey adopts her as his daughter later on.
Maybe it does similar to Angie, but I thought Angie was subsititue for Shadow in the 03 seires, just like Lotus Bloosem was a substitue for Karai in the 87 series.
Also I would like for New York City and maybe even the world to know of the Turtles excistence, and for the general public or at least the adults world to think of them as vigerlantis, similar relationship that Batman has with the public in "The Batman" series.
Other have talked about bring some of the old characters from the original cartoon like Bebop, Rocksteady, the Channel 6 news staff, that is fine with me. But I have another character from the original show to bring back. Zack aka the 5th Turtle. I would bring him back as what he was before, one of the Turtles biggest supporters despite adults saying their vigilantes. I would make his dad a police officer who doesn't want Zack hanging these vigilantes Turtles.