An update - Problem solved for me! I had another watch of the video and another read of the PDF, and realized that I had missed a notation in the PDF. With the X1 V4, I needed to have the brown wires going to the mainboard flipped 180deg compared to the V3 (and prior). The BLTouch started behaving as normal. For some reason, the initial nozzle height was WAY too high on the first layer of my first print, and I had to baby-step it down quite a bit. But, I think I've got it dialed in.
No issues found yet in this firmware, and it works a treat!