quoted

My hope is that we can make use of a well known and uniform
API for all input devices in a device, be it a keypad,
touchscreen, accelerometer, magnetometer, gyro, or whatever.

If only we could agree what input devices are...

Is that the right test for some of these devices.

Surely the question is "what devices can be meaningfully represented by
the input API". 

The device range is always going to be quite large and people want to use
the API because it means things just work. They can wire their home made
surfboard unit and tilt sensors up to the PC and tuxracer just goes. They
can wire pedals and a current meter to it and use it as the speed input in
bzflag to simulate bicycle tanks etc..

Alan