I find this incredibly interesting, but what are we talking about exactly?
You make a great observation, that black metal fantasy spilled over into reality. But how exactly do we incorporate this into the future of metal? It was all unintentional and incidental, as you say.
In terms of the future of metal, perhaps you can actually look to what Immortal tried to do, which was create this whole world, Blashyrk. Obviously it was pretty juvenile, but the rudimentary idea is there. Create a whole mythological world, its stories and its Gods, then make music in tribute to them. It's both a literary project and a musical project, and why not illustrations too and make it a visual project?