I know of no vids that show what I'm talking about, but the idea of the feet together stance just prior to a cutback, comes from not being able to do the things that good longboarders can do. About 4 years ago, I was in the parking lot above Nth Avalon on a sunny day watching a well known longboarder taking everything that was on offer, I did not want to go out because I knew there would be nothing for me.
He had a certain style on take off that a lot of LBs use, he gets an early entry, lifts his torso of the board, surveys the surroundings, pops to his feet, and while they're still close together, throws one foot back, knees slightly bent, leans into a turn and snaps the nose around like it's the tip of a whip, goes bolt upright and trims.
I know I could never do it, pop up too slow, and I'm way too tall to keep my centre of balance right. But it did inspire me to try something similar once I'm up on the board, and only for the cutbacks, not the forehand turns. I even started doing it within a half an hour of watching him, and I kind of think that he may have looked at me doing it. I'd like to think he thought it was my style rather than something he inspired.
The limp arms are just something that appeals to me from still photos, oddly, one of those people is Mark Richards, his nick name was "the wounded Seagull" because of his outlandish arm movements, but somewhere there's a pic of him leaning into forehand with his back dead straight and both arms hanging limp in front of him, I really liked the pic. The second person was one of my favourite lonboarders, Leah Dawson, there's a few pic of her doing it on both the forehand and on cutbacks and to me it just looks good because it's so nonchalant
The most interesting thing you say is " brain is no longer all that connected to my legs and feet" which is almost the identical phrase that I used when I tried to go back to surfing about 7 years ago and nothing would work. The pop up has never, and will never work for me, my left knee is beyond help, but the communication between brain and feet was something that I may be able to do something about.
I made a couple of balance boards and started using them for around 10 minutes a night, and within a week, things improved, I kept that up for around 2 months before I stopped needing to use them and only drag them out when I've been out of the water for 2 or 3 weeks.