Roman getting a long run is likely the company rumors of Rock wanting to come in and work against him. They have to make Reigns look seriously good with a long good heel run to prepare him for Rock next year. Roman should at least hold the title til Royal Rumble where he can drop it and then work against Rock at Wrestlemania if that is the plan. Give him very long run as champion with beating a lot of top guys.
(Personally if it was me I'd go back to 1 WWE World Championship with Roman...but they are still doing this 2 brand champions deal)