I have an idea I'm throwing out ( and releasing any claim to so it could be used ) ...
First, I'm against the idea of cloning Radiator Springs Racers. Beyond just wanting something to be unique to DCA, I worry the ride would lose much of its charm divorced from the rest of Carsland. I certainly wouldn't expect near the merchandise to be moved were the ride cloned and not the entire land.
With that said, I started thinking through how to accomplish what Disney wants (a mega-hit ride like Radiator Springs Racers and a sure-fire success like Radiator Springs Racers would be) while also providing something different and a little more suited for DHS. Something with that would bring the cache that RSR has, but tweaked for DHS. While brewing over this the answer hit me...
Cars - World Grand Prix. A ride that can use the system of Radiator Springs Racers while also providing new sights and scenes. If we're going to get something from the world of Cars, let DCA have Cars 1 and DHS have Cars 2. It works for the ride; you still can have indoor scenes explaining the race, and then you still need the race portion. You can even further strengthen a "Cars Lot" portion of Pixar Studios, all tied together by Cars 2 with the World Grand Prix and an updated Lights, Motor, Action highlighting the Cars 2 spy motif.
The main thing I would hope Disney could incorporate would be a World Grand Prix Jr, an intertwining (or at least connected) Cars-esque Speedway, so all ages could enjoy the fun.