Necrothread!
You guys gotta remember that in the '70s, Stereo was still a newish super-cool feature and if breakfast cereal could have been sold as "Now in Stereo!" it would have been.
I had a Stereo Startfire !V and it was a PITA. The master volume was a double-stack pot and I could not get it out of the guitar because it didn't fit through the F-Hole and I'd have to pull the entire harness to even try and get it through the pickup route. I swear they mounted the pot on the guitar top then built the rest of the guitar around it.
Though the idea was cool because it was different and allowed different things to be done, guitarists aren't known for embracing new things. As a result I've seen more than one stereo-equipped guitar converted to mono.
Also, "stereo" is generally used for spacial separation and that's not what you got with this solution. With a stereo guitar (at least the ways I've seen them wired) you get tonal separation which means the neck pickup in one amp and the bridge pickup in the other. While you could do some interesting things with this setup, back in the day there weren't many (if any) stereo pedals so that meant you'd need dups of everything in your chain.
I'd much rather have a mono guitar split into two paths so I can do things like spacial separation with chorus and phaser, etc., while giving me the flexibility of using two amps. Stereo chorus and other similar effects is absolutely intoxicating. Stereo the way my Guild was wired was not.
YYMV, etc.