Well then get one of those guys on the movie.
OOTS was as far as they could go into the cartoon FW territory, now go back to Eastman & Laird's original vision for what eventually turned into the Bay reboot, Batman Begins-esque Turtle movie. There are dozens of directors & writers out in Hollywood that would be interested in doing something closer to the comics. The original story is more compelling & mature than most of today's TMNT media. A writer would probably find the notion of writing a serious TMNT film that actually strives to be a good movie more interesting than another dumb family film for kids. Getting the people to make the movie wouldn't be the problem.
But, first and foremost, at the moment the money is in the kids series. That's what probably hurt the sequel some what, it didn't look like the current show. Going to the notion of beaks and looking like turtles, kids can't relate to that and mainstream won't pay to see that, i would, ofcourse.
Kids series and nostalgia is the way to continue and you can make each turtle different - a different species - mikey, a sea turtle, raph a red eared slider, don a bog turtle etc. That way each can look subtly different and if we use the face designs from the comics, the original movie did a pretty darn good job.
The supporting cast need to be strong and well written, i want casey jones but it's maybe too soon?
How would new york react if there was an urban legend of TMNT in the sewer? You'd get kids going down there - what if there was a real foot clan, are they henchmen or an actual underground crime organization?
At the heart of it, it's a father of 4 sons that are outsiders, throw in some ninja, some parkour, hint on dimension x, there you go.
I never realized until i started watch the FW cartoon how much of a loon Shredder was, i would love to play that angle where he appears mad, at the end he gets arrested and locked up.
Warden to the detective "he's linked to the whole turtles urban legend, he says he has been communicating with a trans dimensional brain, called Krang that is controlling him along with two mutant beasts, a wart hog and a rhino - what a nut job" they laugh it off, we know it's real but is it really just in his head? Is shredder just some american ninja reject with daddy issues, living in a fantasy world or is it true?
As an edit, i remember one episode shredder went out into the city under cover, basically wore a long jacket and hood, even tho his blades and mask were clear as day, he walked around, happy thinking he was incognito and we could have shoppers look at him thinking 'wtf'