Making a new genre?

I'm curious... what specific elements separate genres from each other and could one simply "come up" with one? This came to me after making my song Firechild. When releasing it, I was asked for a genre to put it into, and I really just guessed. We are fully aware of the catchy pop songs, heavy hitting 808 trap tracks, and the groovy jazz tunes, but what about the sub-genres? What if we were to combine jazz and hard rock, or EDM and rap. Sub-genres are all over the place, but as far as creating a whole new genre that has something everything else lacks seems merely impossible. But nothing is, and one day, I would love to be amazed at what the musical community comes up with.