Very interesting!
With the internal display disabled via this approach, I can close my Surface Book, which turns off its built-in display (sometimes, at least), and the two 4K external monitors will turn on! So this is progress.
However, the 4K monitors switch to 30 Hz, which is quite egregious considering they are not televisions—they are monitors. I tried using my shaved mini-DP to DP cable to connect one of the 4K monitors to the Surface Book's base (while one remains connected to the Dock). This approach continues to not work at all. I suspect that port is actively disabled when the dock is connected. So I now have my 4K monitors running at 30 Hz.
This is a step in the right direction but still unacceptable and not what we should expect. Namely:
- The monitors are running at 30 Hz which is unacceptable. Monitors should run at 60 Hz or higher. 30 Hz is suitable for televisions.
- The internal display must be disabled when connected to two 4K displays. This is clearly not the case in the advertising material (I believe a commercial I have linked elsewhere shows all three displays on).
- Obviously Windows Hello is meaningless with this configuration since the camera is not able to see me. This sucks because Windows Hello is one of the coolest Surface Book features.