TMNT 2 Trailer
It sounds as if Krang is a definite for Teenage Mutant Ninja Turtles 2.
In an interview with Rolling Stone, it's revealed that producer Michael Bay spoke with Industrial Light & Magic about the special effects surrounding Krang.
They start with Ninja Turtles animation. Pablo Helman, a visual-effects supervisor who worked on the Star Wars prequels, appears onscreen and shows Bay the latest version of Krang, a new-to-the-movies villain who is, essentially, a disembodied brain inside a giant robot. "So we've eliminated the tentacles," Helman explains. "Is it too monster-ish?"
"He could have some tentacles," says Bay. "I just don't want them coming out of the side. He looks like a stupid octopus."
The interview continues with mention of the special effects for Bebop and Rocksteady, with the characters already a part of the recent trailer (watch above).
They show him a clip of two other new characters, a mutant warthog and a mutant rhinoceros named Bebop and Rocksteady. "You gotta adjust that mass," Bay says. "That mass is not too good yet." He watches a few more times. "Is our rhino dude's head big enough, do you think?"
It should be noted it sounds as if the interview took place prior to the release of the trailer, so it's always possible Krang could have been scrapped. Hopefully (doubtfully) that's not the case.
Here is concept art that previously hit the net said to be for TMNT 2 of Krang as well:
"Teenage Mutant Ninja Turtles 2" has a June 3, 2016 release directed by David Green and produced by Michael Bay, Andrew Form and Brad Fuller, starring Megan Fox as April O'Neil, Will Arnett as Vernon, Stephen Amell as Casey Jones, Tyler Perry as Baxter Stockman, Brian Tee as Shredder, with the movie also featuring Bebop and Rocksteady.