shows this entry which is key:
# USB support
# CONFIG_USB_UHCI is not set
According to this page, this would have to be set to 'y' in order for USB keyboard support to be enabled:
However, even if the kernel could see and talk to a USB keyboard, we still have a major hurdle: Lack of Cascade support for the USB keyboard. Applications would have to access the keyboard some other way.
Someone outside of Roku built a custom kernel once, right? Are they still active here? Could they try the flag above in the kernel config and see if that works?