Suit is dead. He was only significant as a face for the Set while Telsin was hidden away. But now we know the truth about her, and Wax is most likely about to have his final confrontation with the Set in the next book. So Suit doesn't really add anything to the story anymore. And also, Wax and Wayne are supposed to be mshorter and more lighthearted, and there is a lot to wrap up in The Lost Metal. I doubt we will get a plot with Suit doing things in the Cognitive Realm.
As for the OP, I guess it is possible that the Set came from somewhere else. I doubt it, to be honest. The two main candidates for Trell (the only plausible ones, really), are Autonomy and Odium, and neither one seems to be the type who has a dedicated group of minions following them everywhere. I think that Autonomy hijacked Trelagism, recruited a bunch of Scadrian followers, and started working.