Warcraft as a whole probably would be to damn big and epic for a mere two hour film, but if they ever plan to make it, there's storylines that should be done.
1) The Scourge of Loaerderon, with Christian Bale as Arthas. He's shown in Batman Begins that he can play a character who evolves over the course of years and act all the phases he goes through convincingly. If anyone cna start as a rookie paladin and end up as the self proclaimed king of the dead after two hours, it's Bale. Scarlett Johansen would make a good Jaina. For the role of Uther, I'm honestly stumped. Possibly Mel Gibson but he'd probably try to steal the spotlight in every scene he's in.
2) Lord of the Clans, with his Harlan Hogan voicing some 7' guy in a costume(no goddamn CG. LOTR managed to pull of their orcs without it, other films can try too) as Thrall.