Thanks very much for posting this. I too had read that this was supposed to work but had no success myself. You had been quite specific in confirming that it related to firmware, and I had initially been stuck on an older dock firmware when Microsoft had broken the Gadgets app on Windows 10 Mobile at around the time I bought my Lumia 950.
There is also the question of whether people had tested both DisplayPort and HDMI. I found that in my tests the LED on the HID-500 dock had always remained red for both types of connection, and I only got the charging chime when connecting.
Your post has spurred me to have another try, and what I noticed just now with my 2016 MacBook, is that it didn't work at all until I selected the correct input on the monitor *before* connecting the USB-C lead. I used DisplayPort first, and that did drive my Dell U2415 at 1920x1200 with audio, however after a couple of minutes the monitor would go into power save, disconnect, then immediately wake up again in a loop every few minutes.
After switching to HDMI I don't get this power save issue. It could be a Dell monitor firmware issue, or a HID-500 firmware issue. This same monitor certainly does not exhibit this issue when connected via DisplayPort to my older Mid-2011 13inch MacBook Air, so I think it's probably the HID-500 causing the issue. Anyhow HDMI is fine, at 1920x1200 with audio.
It would seem that the Mac seems to need the monitor to be set to the correct input for that all-important first detection which I'm guessing prompts Mac OS X to install some additional driver - because since then I get the white LED on the dock every time I connect it now, regardless of the active monitor input. The HID-500 charger is just able to power the Intel Core M MacBook, though it can only charge it very slowly.
I'm really pleased with the result. Now my home office desk is ready for me to dock either my MacBook, or my Lumia 950 with a single tiny cable. People have moaned about this USB-C connector, but I like it.
