Bishop and Ch"rell.
 

Will Bishop and Ch"rell ever be introduce in the mirage universe.

Ch'rell sort of was in a Donatello backup story... at least it looked like him... but he was grouped with the Turtles' "friends".

No word on Bishop, but Peter has hinted at Hun crossing into the Mirage universe.

The problem I see with both characters is that being who they are, how do you translate across and not have it make some sort of impact on the state of things in Volume 4?

Surely Bishop would've had some say in the state of the world during Vol.4 if he were to be true to his animated origins. You'd have to make some fairly drastic changes.

eh.. probably have some Tales of the TMNT story introduce him, explian why he's been shut down.. then make his big return in Vol. 4.

I mean, c'mon.. they had Radical at Splinter's funeral, rat King appearing behind Splinter as he died, as well as Leo sparring with Cha Ocho in Vol. 4... and then Tales explains Leo and Radical, Rat King and Splinter, and even how Leo first met Cha Ocho.

All this is true, but the thing is, all these characters were in the comics years ago. They have an established place in the overall story. Dropping Bishop and Ch'rell would mean retcons, and I don't know how ready Pete is to change the rest of Volume 4 to suit the sudden appearance of Bishop. Depending on how Volume 4 turns out, he might be more suited for an intro AFTER that story. Simply putting him in now would raise way too many question for across the board consistency in the character.

Did Cha Ocho appear prior to Volume 4?

If I recall, the Tales issue came roughly the same time. But Cha Ocho isn't really the best example. Comparatively, he's a minor character. People would probably cry foul if Bishop was introduced into the comics as a Cha Ocho style appearance when everything that makes that character who he is relies on big, involving stories. It could be done, but short of drastically altering who he is and the purpose he serves, it could also be a little late in the game.

Maybe Peter could intoduce Bishop and Ch"rell after volume 4 end.

I wouldn't mind Bishop, but Ch'rell.. That would be weird