If he's a face, he can feud with Owens who's wrapping up a program with Styles. There's also Corbin, who obviously needs a feud with Cena now on Raw. There's even Mahal. I wouldn't go that direction and put Roode in a title match already, but it's possible. They only waited 3 months to give Nakamura that spot. If it were up to me, I'd turn Orton heel and put them against one another.
But I think it's gonna be Ziggler. He was finally back on tv last night, taking shots at everyone including Roode, saying something along the line of "maybe if I come out in a robe everyone would like me." It would be a fine way to go, Ziggler can carry on a decent promo and still go in the ring. It's hard to believe, but Roode is actually 3 years older. Roode is 40 years old, so I don't think they'll waste any time in making him WWE Champion. I'd be surprised if he's not already wearing the belt by the time the Rumble rolls around.