I've thought of a couple ways that Klei could implement A New Reign on PS4.
The most comprehensive and least straining way to Sony, would be for Klei to create a "separate game". It would only be available to people who sign up via form to Klei, with a PSN id that could verify the purchase of DST and Klei could distribute codes for the download. It would be minimally stressful on PSN's servers since all they would have to do is host a game and updates.
I'm sure it could even be configured to use the same files even, but what do I really know.
I know I really want to see ANR beta on PS4. My honey and I play a lot together, but she doesn't like playing on PC. (She has to use her laptop and a controller anyway.) But it's always been a smoother experience when we play on console.