Following several requests for information on MonoGame Xbox Support, please read the following before posting.
If you simply want to create UWP projects for the Xbox, you only need to register for the new Xbox Live Creators Program.
For this, you don't need the Xbox branch of MonoGame, just the Windows 10 UWP templates. (targeting the Anniversary build 14393+)
I did a video session on this there:
If you then want to go Full native, you will need to apply to ID@Xbox with a pitch for your title. I recommend starting with UWP, then look to ID if you are hitting the perf wall and have a project you can demo to them.
Remember UWP, gives you access to all Win 10 platforms, from Desktop / laptop / mobile / Surface Hub / XBox and even HoloLoens.
Native only gives you XBox.
Only ID@Xbox developers can access the Xbox Branch of MonoGame and this is granted by the ID@Xbox team directly. Access cannot be giving by asking in this forum.
Note, same applies for Playstation / Wii / Switch or any other platform not covered in the public release.
Access is given through the developer program for that platform