Nice write-up.

I wonder if something similar exists for the Snapdragon X Elite-based Microsoft Surface 7 laptops but is simply undocumented. There's a post https://news.ycombinator.com/item?id=44426428 (The hidden JTAG in a Qualcomm/Snapdragon device’s USB port) obviously about a hidden JTAG, so I begin to wonder.

If someone more experienced with these sorts of things could chime in that would be great.