The USBHIDKbd2MIDI project connects a Trinket M0 to a USB keyboard then outputs MIDI on a DIN connector. However, this can be changed to output ASCII characters instead and adapted for the Feather M0. And replace the MIDI DIN interface with the USB serial adapter. Check the Adafruit schematics and tutorial on powering the Feather M0 via its USB pin. It is safe on the Trinket M0. Note is NOT a good idea to power the Feather or Trinket M0 via micro USB port and USB pin at the same time. Be sure to have only 1 power source connected at a time.
I have never tried the Feather M0 in USB host mode. As I recall, the Arduino MKRZERO does work in USB host mode.