2016 has always been supported, but the Install Anywhere packaging required some smoothing to support some UI changes from 2016 (which is why the remote installer was a work around) and there was a minor display issue once in the console not registering the OS correctly.
All of that is resolved with 6.3.1 Hotfix 5:
I just used the HF 5 local installer on a brand new 2016 server and it ran without issues.
As for the remote installer I would suggest you run it on the same LAN or VLAN in case there's something else blocking it. Otherwise reach out to Support directly (if you're under active maintenance) or your Sales contacts (if evaluating) and they may be able to help with other suggestions.