EDIT: I don't know why. I have 7 years of Gold and I have Xbox One preordered achievement. Might be related.
EDIT2: I also have the highest tier on Xbox Live Rewards for achievements unlocked. Might also be related.
EDIT4: (there is still hope for you who have not received anything yet)
Luck of the draw then I suppose.
Xbox Official Twitter reply
We considered a variety of things like Gamerscore, LIVE tenure, & other factors in markets where #XboxOne is available.
Chatting to Support now to confirm...
And yes, definitely in waves.
Henriette: at 21:41:31
You are definitely correct, we are giving away free gifts to all qualified users all over the regions where the xbox one is available. I believe the emails are already sent out starting today and it is by batch or waves, which is what we have been informed.
Sikamikanico: at 21:42:05
That some good news. :) Kudos to MS for doing something awesome.