I got the message from Support that I could register, I entered the code and registered yesterday, and now the app is telling me that my console is registered to preview the coming updates. Only problem is that there's no difference on my console and it is still on the last software version. I've turned it completely off with no avail. So that's not going to help. I've tweeted Major Nelson and Support to see if they can do anything. I've got my controller connected via USB and it hasn't offered to update the controller either.
But it's just a little disappointing that my Xbox is telling me that I can preview the update, when I definitely am not able to at all.
I also can't access the preview forums, the link constantly tells me that the group cannot be found.