Mine doesn't work too. My Display Dock is not detected by Gadgets app.
Gadgets : 4.4.1609.2000 4.3.1608.28000
OS Build : 10.0.14393.448
Even my wireless mouse is not detected on my display dock. I hope it's just a matter of firmware issue, and it will be resolved by updating the display dock. But i can't update it since it is not detected by Gadgets app.
Please kindly help us with this issue Microsoft.