However, this article does not mention two very important issues. In order to make a circuit board of any interesting complexity (i.e. more than an Arduino and a few LEDs), you need more than 2 copper layers to route your traces on. And, you need VIAs (Vertical Interconnect Access), which are columns of copper that make electrical connections between the layers.
I have used a PCB mill and while it is very useful for making extremely simple circuits, it only lets you mill 2-layer boards, and it does not let you make VIAs (instead you have to manually drill a hole through the board and solder a pin into the hole, and this approach has a much much larger diameter than a real via).
In order to be interesting for "maker" goals such as Linux machines, IoT, and robotics, there needs to be a desktop fab solution that can at the very least make 4-layer boards, with VIAs.