I wondered this myself. However my work got me an XPS 15 at my request (with Windows), and I installed Ubuntu on it. I can switch between NVIDIA and Intel graph

I wondered this myself. However my work got me an XPS 15 at my request (with Windows), and I installed Ubuntu on it. I can switch between NVIDIA and Intel graphics just fine. I haven't tested the USB-C video output though, just the HDMI.