Elektra Natchios (Earth-1610) - Elektra: I believe Elektra deserves more attention, and they don't seem to be doing much with her in the Ultimate Comics as it is. I mean, why not? She's an assassin who once worked for the Kingpin. I could imagine her wanting to repent for her sins, thus she joins the Thunderbolts. Either this, or make her the new Daredevil.
Elizabeth Ross (Earth-1610) - She-Hulk: I genuinely believe She-Hulk deserves much more attention than she has been getting in the Ultimate Comics line. She only appeared in the Wolverine vs. Hulk miniseries, and that was it. Betty Ross was a major character of Ultimates and She-Hulk of the Marvel Comics altogether; so it's just kind of sad that we're not seeing her more. Putting her in the Thunderbolts seems natural to me.
Eric Brooks (Earth-1610) - Blade: Blade was apart of the Ultimate incarnation of the "Avengers" and battled against the New Ultimates. I would like to see him appear again in an Ultimate Thunderbolts team. Bounty-hunting, vampire-killing...vampire? Sounds cool to me. Joining the Thunderbolts seems like a logical next step for him.
Frank Castle (Earth-1610) - Punisher: He would be a principal part of the team: perhaps its leader, even. Faced with the burden of killing Peter Parker, I think the Punisher would reluctantly agree to sign-up for the Thunderbolts; it'd be a pseudo-way of making up for murdering Spider-Man. He'd be the silent, grim member of the team.
Frank Simpson (Earth-1610) - Captain America (2) (Vietnam War): An insane Captain America. What more do I need to say? He's the exact opposite of the real (or "first") Captain America. I think some kind of story-plot would suffice to permit him joining the team.
John Blaze (Earth-1610) - Ghost Rider: Again, this is another character that I think deserves more attention. I don't see him carrying his own series, so putting him in with the other Thunderbolts sounds okay to me.
Petra Laskov (Earth-1610) - Red Wasp: Once apart of the "Avengers". I'm not sure what happened to her, but it'd be great if they brought this character back. She has a dark past and I like the ruthless personality she possesses.
Luke Cage (Earth-1610) - Power Man: There's not much I know about this guy, but if they devoted more focus to his origins and personality, I could imagine someone like him on the team. He'd be this team's Hulk; well, besides She-Hulk, of course.
Silver Sable (Earth-1610) - Silver Sable: Bounty hunter who stops at nothing to capture her target; played a main role in the original USM comics. If they're not going to use her again in UCSM, why not put her on the Thunderbolts?
Wadey Wilson (Earth-1610) - Deadpool: And we come to my favorite member of this team: Deadpool. Originally an anti-mutant extremist. I think if they ever reintroduce Deadpool to the Ultimate Comics, make him more like his original counterpart. I think he deserves to remain the same, regardless of whatever universe he's in. I can imagine Deadpool making some clever banter about the team, and them despising him for it.
Zarda (Earth-31916) - Power Princess: I just felt like adding her on the team. I don't think she's doing anything else of extreme importance right now.