DarioPennisi:
I am afraid Limba was too fast in answering...mini PCIe pinout allows for several alternate pinouts and one of those has USB on it. PC motherboards usually support both PCIe and USB modules (for example most GSM modem mini PCIe modules use USB, not PCIe) so you'll be absolutely fine fitting Vidor in a PC, provided you have a mini PCIe interface available and you remove headers.
once you have Vidor fitted you have a choice to implement your USB to SPI bridge in many ways. maybe the easiest is to just implement a serial console that gets commands and uses SAMD to drive SPI.
This is interesting, but consider that i need to develop hard real time applications:
I'd like to apply this systems to CNC machines.
In this field the usb is good only for handwheels.
G.