FWIW, I was poking around at a different local Dodge dealership than my usual one (I can only go there on Sunday because they're so sleazy), and there was a sold green 3500 quad there, ready to go, and it had a reese 5th wheel hitch installed in the bed. Looked like a used hitch. Couldn't see very well how it was attached (it was a 2wd so it was pretty low).
To be honest, I think you're all panicing. Dodge makes a big deal about how these trucks can tow heavy. They tested them by pulling a large concrete block on a gooseneck trailer. And I bet that they are still only rated to tow 10,000 lbs with the bumper pull hitch. Therefore, to achieve their 16,000 lb tow rating they must be gooseneck/fiver compatible. Maybe it will require different mounting than we're used to, but that shouldn't be a big deal.