atmega32u4 combined with usb host shield (MAX3421E)

Has anyone ever had a USB Host Shield working on the atmega32u4?
I would like to have a combination of a "usb in" with "usb out" to make a hardware keyboard mapper.
(receive data from usb keyboard over the usb host shield, fiddle with some bits, send to the pc over the atmega32u4 as usb hid keyboard)

I see the usb host shield is connected as an SPI device and the atmega32u4 supports SPI.
But perhaps there are other limitations that prevent this from working?