alt Hacker NewsAt the end of this video they link to another video from a year ago [1] (this is the same link as the comment you were commenting on, whoops), where they recreate the sodium vapor process with a rig with a beam splitter, one side had a filter to reject sodium vapor light and the other has one to reject everything but sodium vapor light, and then a camera on each side.
The Disney process had the filter essentially built into the beam splitter, but afaik, nobody knows how to make that happen again (or nobody who knows how, knows it's a desirable thing). Seems like the optics might be cumbersome, but the results seem wortwhile.
Also, you need still need careful lighting, you don't want your foreground illuminated by sodium vapor, but I wonder if you could light the background screen from behind (like a rear projection setup) to reduce the amount of sodium vapor light that reflects from the foreground to the camera.
We know how to make dichroic prisms (Technicolor used them when filming, as did "3 CCD" digital cameras), but I imagine that to have a sufficiently narrow rejection band for the sodium-vapor prociess, you would need to be smart about where you place the prism, since the stop-band of a dichroic filter changes with angle of incidence.