Who's to say this couldn't become an epic trilogy? The story could be split between the two factions: Two guilds crossing paths and working past major confrontations (with each other, Bosses, etc).
Which big name actors do you think could pull off a believable representation of the classes/races in the two guilds?
Christopher Walken (undead priest)
Angelina Jolie (blood elf rogue)
Kristen Stewart (CGI gnome mage)
Arnold Schwarzenegger (draenei warrior)
James Franco (human hunter)
You get the picture...