I did know that in the Japanese language, Primal Dialga was known as Dark Dialga, but did not know about the other stuff... But I personally feel that Game Freak shouldn't just disregard Primal Dialga in the remakes. After all, one can't deny that Primal Groudon and Primal Kyogre share a very similar design theme to that of Primal Dialga. I even dare to say that Dialga is where the two got their own primal designs from. I do think that it would be outside of their comfort zone for Game Freak to put Primal Dialga in the remakes, as they would have to come up with a design for Primal Palkia that would sit well with Explorers of Time, Darkness, Sky fans. But it would be somewhat beneficial for business purposes-as it would attract many people whose hearts lie with the Mystery Dungeon series and don't play the traditional games as much. Also the two would probably not be as op as Primal Groudon or Primal Kyogre, as their abilities would likely stay Pressure(Dialga because that's how it was in the Mystery Dungeon games, and Palkia to match Primal Dialga), though it is of course Game Freak's decision to make. But that's enough theorizing for me-honestly, I think the possibilities of the two getting primal forms in the remakes remains roughly 50/50.
In addition, I don't view the Mystery Dungeon series as canon to that of the Pokemon main games. I view them more as alternate dimensions(so basically, different game cartridges according to Game Freak :3).