Whenever I hear the term "edgy" being applied to a new re-envisioning of a character, I'm always quite very apprehensive, since it often doesn't work out very well.
This being a Bay film, the action will be made of up of lots of closeup shots with a shaky camera, making it extremely difficult to follow. Probably throw in some useless offensive stereotype characters as well.
I will not comment on Bay films because I hate them, but making an original story darker works sometimes. I'm a big fan of the 90s animated series of Batman which was very near of the film noir genre. It was way better than the silly series of the seventies (I think) even if it was funny. But I agree that making the ninja turtles darker is hopeless. Those are turtles who are ninjas and eat pizzas. How this can become serious?
TMNT was serious/violent in the original comic books. It was serious/violent (ironically) as they were a parody of contemporary violent comics like frank millers ronin. Remember they were wielding swords, daggers, nun chucks, staffs which some how never really cut/blunt force trauma any one. Then as the cartoon ran longer things get lighter, clan foot soldiers are now robots, Michelangelo never really uses his nun chucks and starts only using a grappling rope ect.
As the originals were black and white a sin city re imagining might be a cool idea, Bay is not the director for this though, he's no del Toro/Robert Rodriguez.