I don’t think voxel engines need to work with only voxels. The environment could be, but animated models should probably still be polygons. So the challenge is

I don’t think voxel engines need to work with only voxels. The environment could be, but animated models should probably still be polygons. So the challenge is you don’t just need fast voxel rendering, you need fast 3D rasterization into an optimized data structure (like sparse voxel octrees). I don’t think this will pay off until game engines do absolutely massive amounts of physics and lighting simulation. But I think it’s inevitable. You’re already seeing indirect lighting engines using low resolution sparse voxel representations of the world.