It appears The Hollywood Reporter jumped the gun on the Underworld reboot news or Lakeshore Entertainment had a change of heart. Just a few weeks ago, they reported that Underworld was gonna be rebooted, but today Lakeshore Entertainment is developing a fifth Underworld film that will be "expansion of the existing universe." And how will they go about doing that? They're gonna hand over the keys to the franchise to Theo James ("Divergent"). He played the role of David in the previous film, Underworld: Awakening. David is/was Selene's protege and is a Vampire-Corvinus Strain Hybrid.
"Sources say there was an option on James because of his work on the previous film, and he'll star opposite two new female characters. Casting is underway for those roles, with plans to start shooting in the spring." - The Hollywood Reporter
Underworld Awakening - Kate Beckinsale, star of the first two films, returns in her lead role as the vampire warrioress Selene, who escapes imprisonment to find herself in a world where humans have discovered the existence of both Vampire and Lycan clans, and are conducting an all out war to eradicate both immortal species.