You are wrong. But let's assume for a second that Xenoblade can't be in the original, but can in the "new". Could you elaborate on why?
What makes the "new" model more suitable for it? It's probably not the RAM, since the Wii has less ram than the original 3DS. It's probably not the gpu, since the gpu is exactly the same between the two models. It is not the video ram, because it is the same as the Wii's as well IIRC.
So that leaves the 2 extra cpu cores, after removing a percentage for the improved 3d, which needs to recognize the face, follow it around, and readjust the 3d in real time.
Does it make so much of a difference? And even if it does, why not just reducing a little bit the viewing distance for example, and make it available on the original model?