Lord of the Red will likely be his Signature Card for his Starter Deck since Red-Eyes Darkness Dragon requires you to tribute Red-Eyes B. Dragon to summon it. So that's likely either a drop or a Level-up reward.
Actually never mind, got my facts wrong. Don't remember GX too well. Guess he'll use Red-Eyes B. Dragon and Red-Eyes Darkness Dragon in his Starter Deck. Dang, 2 URs in the starter deck is kinda crazy. lol
I'm thinking more along the lines of Red-Eyes Darkness Metal Dragon. Sure, it's incredibly powerful, but we don't know how the metagame looks like when Atticus is released, and you'll very likely only be able to get 1 REDMD and no more no matter what.
They could just give him Red-Eyes Darkness Dragon and not Red-Eyes B. Dragon in his Starter. They did it with the Paradox Brothers and Gate Guardian. Also, you're guaranteed to own at least 1 Red-Eyes B. Dragon before unlocking Atticus anyway since you have to unlock Joey prior to unlocking GX, so it isn't a huge issue to do this.
Actually, another thought: They COULD pull a Polymerization and give Atticus a Red-Eyes and remove it from the shop since that would mean 3 people give Red-Eyes. (Joey, Rex and Atticus.)
Darkness dragon might just end up being a level up award or tied to a skill. While lord of the Red will likely just be in a random pack later down the road.
The bigger question is His joker "Red-Eyes Darkness Metal Dragon". And rather or not it'll be his level 40 award.