As I said this is just a thought but I was looking over some of the threads, mostly ones about boon saying someone will be unlockable. I've read many threads saying who boon is refering to. so far it's been mostly about Sektor.
if sektor is one of the SUs then who are the others? a robotic figure was one the original selection screen, said to be sektor. I think that there might be a chance the other characters who were on the screen originaly but not anymore could be the super unlockables. Or maybe not. midway is known for giving hidden hints, we just have to find them. i hope i'm wrong in this theory because there are some people who i'm hopeing to see in the SUs.