Tip for Hardware modder:
The ideal wireless keyboard for Prime4 is:
trust Tacto Wireless Entertainment Keyboard with Touchpad.
I modded my model for mouse functionality to work with prime4.
Simple unscrew the keyboard, take off the touchpad.
Turn it by 90° - Glue it on top of the touchpad hole.
Because it is´n a square, you have to glue it on top. But it works 
And if Denon recode its USB driver to swap x/y … I will buy another cheap USB keyboard with touchpad.
If I had have more time, I could easily build my own keyboardcase for the components.
because the whole keybord is modular. you have a complete pcb with its keyboard,
pcb with touchpad, pcb with led, pcb with controller
easy to mod … maybe you could buil it into your case, too 