Protocol/CDC to FTDI using host shield.

The Lenonardo uses USB CDC, and can act as a peripheral/slave device on a USB channel. The USB Host Library 2.0 has the CDC(FTDI,Profilic,ect) drivers that should be able to send serial data on USB depending on the device its talking to(what chip it has).

I have another ongoing thread on a different subject. But I was curious if the drivers for the USB host shield using an UNO would be able to communicate with the Lenonardo? Or am I not fully understanding how the Leonardo works? I know it is using a microcontroller for its serial communication instead of a specific chip, but how would that effect things?

The Leonardo uses CDC ACM profile and the USB Host Shield library has a driver for that, so yes, the UNO with a USB Host Shield and this library should be able to communicate with the Leonardo if you choose the correct driver. The USB Host Shield library is not able to detect the correct driver as a PC would do and there wouldn't be enough flash space for all drivers anyway.