Listen to this idea without prejudice:
What if the World of Warcraft film was to simply drop the "Warcraft" name from its title?
Why I believe the film isn't going to work: the associations the general public with video games are awful. There has been turkey after turkey made out of video games. With Warcraft in particular, those associations are especially negative. Talk to people who never played the game and you will usually get game addiction mentioned or that episode of South Park, and the term "nerds" will come up. These aren't good selling points. Warcraft has about the same branding potential as crack cocaine addiction.
I don't believe at this point that any one will be that curious about the film other than players and maybe young kids who haven't yet acquired any prejudices.
So, here's a radical idea. Don't mention warcraft in the title. Films with monsters, CGI and epic battle scenes do pretty well by themselves. And you can still get the warcraft player base to come along by communicating with them through the game client and warcraft media channels.
For a work of fantasy Warcraft has some unusually strong storylines and characterizations. People who have no interest in the game who asked me to explain my interest have frequently there enraptured if I mention the actual lore to them (something I don't do generally except when people won't take no for an answer, just in case you think I stand there at parties boring people). More than once people have said things like "I had no idea a video game could have that kind of depth". Maybe you've done this for yourself: I notice demographics that mostly never play immersive video games like young women become fascinated with characters like Arthas. Remember films like Twilight have dark, supernatural content not that far away from the warcraft mythos (and no I wasn't I fan of those films, that is not the point).
If you can translate that appeal to film then I could think you work past people's superficial impression of the game and its universe and get millions of new players.
Now I know why this won't happen. Some accountant is sitting in an office talking about units and crossover potential from film to game. That will not occur, because no one who has already managed to avoid exposure to the game will be converted to the game by the film. They might if they saw it but they won't go and see it. Even if they do, the knowledge that "it's a video game" will give them a powerful self-fufilling reason not to like it so they won't be a nerd. Maybe some older players will come back, but that's it.
If people really love the film, and then discover it is a video game, it is a different matter psychologically. It is much easier to hold onto a preconceived notion, than form an opinion and then contradict yourself internally.
So, do you think there's some truth to this? If not, why not? Curious to know other people's opinions.