From the last tweet I've seen from Duncan he was still not sure if a sequel is going to happen. He's been working on another movie for some time so maybe we'll hear something soon. I wouldn't get your hopes up that we'll actually get one though, despite its succes in China it still lost money and its overall reception is quite negative. Warcraft may not be the worst video game adapted movie, but its certainly extremely flawed with a lot of potential wasted.