Maybe have two or three intermediate stops if Amtrak does this. As said before, doing stops very frequently on this long and windy route will make the service a big waste of money, as it will be significantly longer than driving.
If it's almost a straight shot from NYC to wherever and back, with one or two stops in medium to larger-sized towns along the way, it can be faster than driving to NYC with traffic, but still still be slower than driving to NYC without traffic. A good improvement!
If there's demand to have local service after the city-to-city is implemented, then you could have NJT hop on and do so. But I doubt that demand will happen fast, if ever.