I guess enough has been said on the subject of SVOTI, I’d just like to add one clarification: Technically, the new GI feature in the CE (which btw is still experimental and active WIP) is called SVOGI and only calculates a diffuse contribution (for specularity you still need environment probes). This is what has been used in Kingdom Come, and this is what the runtime costs of about 4ms are related to. SVOGI has several quality modes, the lowest one only voxelizing opacity and using a single light bounce, while the higher modes calculating multiple bounces and also voxelizing e.g. albedo and normals.
The underlying advanced (and even more experimental) system is called SVOTI (for total illumination) which also calculates a specular contribution. This was used in the Baron Haussmann demo you had a look at, and yes, it is heavier (although not as heavy as VXGI).