A new release of this experimental viewer is out: 18.104.22.168 – Feature Update.
This version has the Volumetric Lighting. It also has a change to how video memory is used. Both of these changes are something people have been interested in for a long time. The memory change could reduce texture thrashing(repeated render sharp, blurry, sharp…). It may be a big aid to those with newer video cards and lots of video ram.
Niran warns at the beginning of his announcement that you need to pay attention to your video memory allocation settings to avoid excessive texture thrashing These are in-viewer settings so I suspect you can live with the defaults Niran has set.
The announcement: Black Dragon Update 22.214.171.124 “Feature Update”
Inara goes into detail about the viewer: Black Dragon 126.96.36.199: “volumetric lighting” and more. She has images of the new controls in Preferences and a video showing Volumetric Lighting.