Have you found any voice lines for Marik Ishtar? To me, this just looks like more "Let's datamine and release any and every new DM character that we can while ignoring the fact that Marik has been in the files forever." I like Duke, though.
Having lines for a card doesn't mean they drop it, so Shinato being a box UR is completely irrelevant. It's like questioning Kaiba having one for Blue-Eyes Ultimate Dragon.
Admittedly, picking a signature card for Noah, if he were playable, would be difficult. But they could just use another Spirit monster like Amatersau or Yamato-no-Kami I guess. Or just say screw it and use Shinato anyway.
Where is your proof for this buddy? As excited as I am for this to be true, words from one random person mean nothing unless there is some kind of evidence to back it up and I would really like to see it.
If anything, Blair is more "confirmed" (as "confirmed" as Duke anyway) than Noah and Rafael right now, as we have a video proof for Hassleberry's line that mentioned Blair. (Check Justin Taylor's video in Youtube)
Meanwhile, there's still no proof for Noah and Rafael. People are just saying things without telling us where to find the proof.
I can't find that video, but simply mentioning a character sadly doesn't mean said character will come as Judai mentions Hayato in Matengo 2 - Hero City when he activates it but there's no indication of playable Hayato whatsoever.