If by platform you mean the underlying structure, which in the forementioned Challenger is the LX, then yes it is a good starting platform, and the same platform the Charger is based on.

The Challenger is NOT that different from the Charger at all. They might look different, but I imagine the weight difference is not as much as you might expect, and since it has the same brakes, same engine, same everything as the Charger, I don't see how its THAT much better of a starting point.

And btw, I am not sure if it is mentioned in this thread, but from what I hear, this concept is based on the LX platform, not the LY, so it could theoretically be closer than you think...