See rom/hidd/keyboard and rom/hidd/mouse.
I've thrown away private CMD_HIDDINIT from keyboard.device and gameport.device, now these devices use new keyboard and mouse HIDDs as underlying level. Actual driver HIDDs may be plugged in or removed at any time using AddHardwareDriver() and RemHardwareDriver().
The API can be further expanded if one day we want to implement OS4 amigainput.library or something like that.
There can be not only multiple input drivers (feeders), now there can be multiple input listeners. So, lowlevel.library can also work on top of the new API and receive events on its own, independently of keyboard.device and gameport.device.