A few metal genres/styles/scenes I'd like to see become a thing.
Metabilly - Basically rockabilly's and psychobilly's metal cousin, influenced by bands like Volbeat. It would have at least three distinct subgenres, such as thrashabilly, deathabilly, and blackabilly. Thrashabilly would be an even heavier version of metabilly. Deathabilly would be metabilly with death metal influences. Blackabilly would be metabilly with black metal influences.
Digital metal - Imagine if bands like The Prodigy, Pendulum, Celldweller, etc turned into full fledged metal bands. Digital metal would pretty much be an offshoot of industrial metal (just like cyber metal). It would be metal music with heavy emphasis on EDM genres such as house, trance, dubstep, drum n bass, hardcore, etc. Zardonic would be a fine influence for this sort of movement.
Brutal thrash metal - Even though BTM is a very selectively used term, I'd love it to be whole new style of thrash metal. Bands like Demolition Hammer and Morbid Saint would be prime influences for this sub-subgenre. It would be unlike death/thrash metal because while that is just thrash metal mixed with death metal, brutal thrash metal is thrash metal put to it's highest extremes.