I think Dragon Ball Daima will have a twist main villain.
I don't think the final boss will be Gomah. They've already foreshadowed that Gomah could gain unbelievable power with the Evil Third Eye, but having "unbelievable power" be tied to an artifact that needs to be equipped and can be lost makes it ripe for betrayal and subversion.
The way I see it, there are two main candidates for True Main Villain of Dragon Ball Daima.
The first is Dr. Arinsu.
She's the most obvious choice. She's an evil scientist with a design that is reminiscent of Towa. She's also a Core Person, the sister of the Makaioshin. And she's been shown to be sneaky and scary already. If they want to canonize Towa, or something like her, Dr. Arinsu is the best bet.
But I think she's a red herring. I think she will have a moment where it looks like she'll be the True Main Villain, only for it to fall out from under her.
The second is Neva.
Yes, the geriatric old man Namekian. I think Neva will be the twist main villain of Dragon Ball Daima. The first episode set him up as this stinky old grandpa, until it revealed that he's actually extremely powerful in Dragon Ball magic, able to sense, summon, and restore Earth's Dragon Balls. And also extremely knowledgeable.
Also the episode subtly revolves around him. Gomah can't use the Demon World Dragon Balls because all three of them are guarded by Kamen Rider-looking creatures called Tamagamis. I think the Tamagamis are obviously going to be mini-bosses for Goku to fight near the end of the series, but it should be remembered that Neva created both the Dragon Balls and the Tamagamis themselves.
In order for Neva to create the powerful Tamagami warriors, he must have used some very powerful creation magic indeed. These are guardians that Gomah, the current Demon King, is terrified of, and they bow to Neva. No-one has made a wish on the Dragon Balls for a long time because of those Tamagami warriors, and that presumably includes Dabura, back when he was Demon King.
The episode also makes multiple references to Namekian lore, almost like it's an important plot point.
Neva says that he hasn't seen a Namekian in thousands of years. Thousands. PLURAL. That's insanely long-lived, even for a Namekian. The climate catastrophe that Kami was sent away from only happened 500 years ago. He did this favor for Gomah in exchange for having 1000 more years of life, presumably this isn't the first time he's made deals like this to artificially extend his lifespan.
My assumption is that collecting the Demon World Dragon Balls is going to be Goku's main quest in the Demon World, for whatever reason. And I think Neva has some grand master plan, where he created the Tamagamis and sealed away the Demon World Dragon Balls for some reason, and now that he's met other Namekians and the Evil Third Eye will be found, that will be the moment he's been waiting for.
Also, he just gives me creepy vibes. Maybe it's the black rings around his eyes that make it look like he knows more than he's letting on. Maybe it's the fact that his eyes turned red when using magic, or he let out an evil cackle when restoring the Dragon Balls.