In terms of Metal becoming mainstream, I'd say no and no. When it comes to public things like the News you'd never expect to hear metal on there, and certainly it wont ever happen except for maybe some special occurrences. Its clear that pop and hip hop are the kind of styles that dominate the music industry today, and its understandable why it is happening as well.
If Metal would want to be mainstream I'd say it would need alot of effort from promoters or bands but theres also the fact that the general audience in the world tends to like the current mainstream genres and quite likely they are aware of the metal genre and probably have heard it, but they didnt like what they were hearing and they'd never wanted to check it out again. So I'd say Metal would have to sound more melodic and uplifting with electronic stuff and a pop-influenced sound in order for it to be appreciated by the larger music audiences in the world today. But quite likely this is not going to happen, since bands want to stick to their sound and not change their musical directions just to reach a larger audience. I know plenty of bands who does it for their souls than for making money out of it, and certainly these bands wouldnt care who are their audiences or how large they are because they know are unlikely to have a wide one anyway.