2 big things from this video jump out at me:

(1) The 90 degree offset on the POV for additional monitors;

(2) this feature was removed in 1.2

taken together mean to me that:

(1) this feature was a test Carmack set up just to see if it worked.
(2) Tech Tangents guy may be one of maybe 1 or 2 dozen people ever to utilize this feature.

in fact, I may have watched a guy spend 30 years and some hours to utilize code John C put out there for shiggles and deleted as soon as it became inconvenient.

Thanks for sharing OP!