It seems like this person is incredibly intelligent and resourceful. Why not just design a new PCB for this instead of modding one? Surely the component cost of 2 connectors and a little PCB could still be in the < $20 range and actually output good quality analog signals? $20 is the same as $3 if you’re also buying CRTs just to play Switch games. This is such a hobby level activity I’m sure people would love a kit + a guidebook, could even provide a 3d printed case.
I think you misunderstand the obsessive, blissful, motivations of a nerd. :)
I was like this when I was younger, where a goal like this would entirely consume me, regardless of practicality, and more of a "see if I can". Some of the best days of my life, where I was most alive, were those times of complete, detrimental, obsession. As I grew older, and patterned by employment, it slowly faded, and sometimes I miss it so much.
(funny enough, I was once nerds sniped about a grids of resistors, to understand PCB trace resistance better, for high currents, because an EE said my intuition was wrong. I made a paint program where you could paint/paste an image, with red being + voltage sources, blue being negative, and greyscale being resistance, and it would show you the current flow through whatever you drew. I was able to prove that my intuition was actually correct!).
To reduce e-waste? Not everything has to be optimised on time or money spend.
Maybe the chips aren't available, or maybe they just wanted to tinker.
Sometimes it's fun to mod something that other people can also easily buy and follow your mod recipe. It's more of a network effect than publishing Gerbers and a BOM.
For example, there are (or maybe were) lots of cheap LED controllers that use proprietary phone apps, but if you crack them open, you find that they're ESP-8266-based, and if you can find the right locations on the PCB, you can reflash them with WLED.