#7 Batista

A second returning legend isn't out of the norm for a Royal Rumble match and few stand out more than Batista. The Animal appeared on SmackDown 1000 in October, teasing a future match with Triple H.
The Game subsequently suffered an injury at Crown Jewel a few weeks later, so we don't know if those plans are still in place, but Batista by all accounts wants another run, and a Royal Rumble return would be a good start for him, and he could erase some of the lingering ghosts of 2014.
Whether he's facing Triple H at WrestleMania or not, a Royal Rumble run would be a good way to begin a new feud for him. Interactions with Randy Orton would also be something to watch closely, though no one in their right mind would want to see those two go at it at WrestleMania.