He's the biggest badass with a knife the lore has. He ties into at least 3 characters backstories. He could offer an interesting take on the Noxus lore...it just seems a missed opportunity he hasn't come into the game yet. Even if they do him like Reaper from Overwatch, where it's not really a mystery who is behind the mask, it'd be cool to see him.
Marcus is either super, super dead, or he's been kidnapped for a very, very long time.
If he were to come out, he'd also probably have a similar style already to Kata or Talon.
Personally, I think it's fairly unlikely, but if he DID come out, I'd like to see them focus more on the General/Tactician aspects, but maybe with some kind of weird mutations or something based on what the Black Rose did to him. Just an idea, though, certainly not canon.
I doubt it.
He was described as a master with the blade and a top assassin....but we have already a blade master 
and an assassin 
in the game
I can't see him coming in the game, no. Firstly because I consider Kat better than Marcus lorewise. She has his knowledge and everyone else's as well as a tone of experience not to mention she's still alive and fighting. Military and political leader, head of her house but at the same time searching the truth, opposing to Swain and his dark methods. Also, Kat and Marcus may both be militaries but to the core they are assassins. They would have similar gameplays as well as with Talon. All master assassins, masters of blades, same thing. I'd like to see him in lore but not as a champ. And I believe Kat has long been placed under his shadow. I've always thought of her as something like Altair. The best but still has to learn. The best, however.
We have two du Couteau champs already
I dont think he will be added to the game. Same reason why the King of Demacia will never be added. They are too high profile to fight and die in the League. Imagine a King giving up his responsibilities and fighting in an arena all day. Prob not gonna happen :P
MAKE HIM THE DAD SOLDIER 76 OF LEAGUE!!!!!!!!
