While there's lots of speculation surrounding monetization in Diablo: Immortal, the team doesn't know how it will work. This is such a hotly-discussed question, we've pasted the reply below:
We don’t know yet. It’s something that we think about, and there’s lots of discussion around it, because we know it’s important to players. We know that — I’ve heard a lot of speculation about what it might be. We even heard speculation that we already somehow know, but we’re just not willing to talk about it. But it’s a hard problem, because we have a very broad audience. We have existing Diablo players who are interested in playing all things Diablo. We also want to bring new players and share with them the joy of playing Diablo. We want to take the time to get it right. We want to take time and figure out what makes sense for the game and work through all the little details to make sure that we get such an important question correct.