Since Nissan hasn't released any specs, this is all conjecture. FWIW, here is my guess. The engine is capable of hauling quite a load. That isn't going to be the limiting factor. I think Nissan will be shooting for 15,000 pounds and be marketing the truck as both a consumer and commercial vehicle. The new f-150 has a payload capacity of 3000 pounds or so, which puts it in first place among the competition. Towing capacity is around 12000 pounds with some versions, which also puts it in first place. I fully expect Nissan to match the payload capacity and exceed the towing capability by at least a ton. The fuel economy of the Nissan/Cummins will better anything out there (especially while towing) that has the capability to tow anything or haul anything.
FWIW, the new RAM diesel barely has the load capability to handle 4 big passengers and a big dog. Nissan is just not going to do that. The Dodge is geared towards people who want the most mileage they can get out of pickup and carry or tow a modest load. The Nissan will be be geared to people who want to see awesome fuel economy in a pickup that is designed to handle quite substantial loads. Can't wait to see what happens.