Music is like language in that it is constantly evolving. Genres aren't fixed. Rather they merge and develop into other things. That's why there is always so much debate about whether ABC band plays XYZ or 123 genre.
As to what the next big thing will be, who knows. Listeners will know it and follow it when they recognise/need it. My OH is currently in two bands playing forms of blues - one very upbeat and the other a very hard, raw, angry sound. Both are enjoying a modicum of success locally. That may be something to do with the economic climate. Whether it's the next big sound, we can't say.