I don't see how TC makers can make them any bigger than this. If pickups start having more cargo capacity, they will bang into commercial truck laws, so a one ton isn't going to start hauling 8-10k in the bed because of this.
I wouldn't be surprised to see some innovation in making rigs lighter while retaining structural integrity, perhaps tossing wood and going with aluminum (like Camp-Lite's models), tossing a combined water heater and furnace for a Truma unit, and so on.