The "Zero" variants of boards tend to allow power over the OTG port, so you can do some interesting things. (Of course, annoying if your powering-device resets power to it). Particularly, if I didn't suck at DTS/u-boot stuff, you could make a PiKVM for <$75. (You can get $10 1080p/60fps HDMI capture cards, you use the OTG port for kb/mouse).

Still, even if you had to external power it, those little boards have pins for power in. It would still be cheap/fairly elegant. And or a USB-C Hub should power it, and give you a place to put more non-host usb devices like a usb-eth dongle.

I would like to make one with some of the (Raspberry|Orange) Pi 3, but again, I've lost too much of my life to dts/u-boot stuff. BSP/mainline woes. It's just easier to be a software-only, cloud-machines-only guy and live minimally.

This article was exciting because I'd love to imagine cheap old laptops being salvagable as little KVM instances, but it seems like OTG/xDCI is just not a priority.