Maybe NVG will use the same style of spyder gear diff in the new tranny as they did in the NVG t350 trannies used in the other 420A cars. if so, then the quaife should just drop in.......if not, I am sure something else will come up soon.
Phantom grip will probably release a product. They have one for the 1st gen neons, and most other dodge cars. I had one in a T1 shadow and it worked great. They go for about $250 and don't involve replacing the diff. You do, however, still have to remove it. Basically, you stick their device inside the diff, and pop off some pins. It expands inside the diff (with heavy duty springs) and "closes" it.
For longevity reasons, I have heard people say you shouldn't put it on a car intended for autocross or other highly twisty driving because it increases heat and friction in the diff when you turn, forcing one wheel to turn more slowly than the other.