Ahh great question - the original brief was:
Filler flat thrill ride to increase quantity of rides/experiences throughout the guest's day
Something different to neighbouring parks
Good capacity to keep up with the rest of the park's demand
Compact
Back then when Doomsday opened, the Mavericks/WB Exhibit building was (and is) still a big question mark sitting in the middle of the park. I'd address that building and its use in advance and plan accordingly.
If the space will serve as the entrance to a wild west themed dark ride that's housed inside that building as well as a flat ride, than a Zamperla Super Air Race fits the bill perfectly. It's compact, good capacity, a thrilling flat ride and it's got a competitive advantage over Pandamonium in that the central mast moves up and down. Given the space is land-locked by two show buildings there'll be a real sense of speed when those things whip around inside the space.
If the entrance to the Mavericks/WB Exhibit dark ride is going over to Arkham's side, then you have more room to play, and I think more room to go balls deep with something folks have never seen before. Let's be honest, mostly everything has been done, seen and installed at this point so you want to capture folk's imagination like Wipeout did back in the 90's. Therefore, i'd risk it for the biscuit and go to Mondial to build either an Airstrike or an Avalanche. My money's on the Avalanche though, high capacity, completely batshit insane and unlike anything really anywhere else in the world, and is visually mental enough that word of mouth would be the marketing campaign, much like Rivals.