Um.. have you been to SFMM? They added two 4D coasters in X2 and Green Lantern. Two similar loopers on Scream and Riddler's Revenge. Besides, Premier Rides is more than capable of building just about any type of launcher SFMM requests, and they've done dueling concepts before.
I have, and while I have had the issue of not being able to go to SoCal theme parks as often as in the past (for issues I will not disclose); I don't see the similarities in Scream/Riddler and in X2/GL.
For me, I call Scream and Riddler different in how it's seating differs from the parks other traditional Sit-Down coasters. And that I consider X2 and GL different in how it handles the 4D spin; whereas X2 is controlled spinning, GL is Freespinning (not that I'm going to give Green Lantern any praise, as I hate that coaster with a fiery passion).
I haven't been able to ride Full Throttle, but I am going by classifications and statistics on that. And I have not ridden Twisted Colossus, but have heard amazing things of the coaster from people I talk too. And that I am hoping to eventually get back to Six Flags to experience the new things I've missed. But that, it won't stop me from discussing and speculating (or hearing particular rumors and possibilities).
That said, you have given a good introduction to IU; as I've had to think of what to say. And that, I can't wait to see what you post next.
That said..back to Premier Rides, if they go with them; then the only thing that I can think of, is more of a Skyrocket II, as it hasn't seemed of them doing anything else really unique with their coasters since 2013 (with FT at Magic Mountain, and Deep Space from an theme park in India).
Why should I think that they change now, especially with mostly everything they've been doing being the SkyRocket II model?