What about Neverwinter(?). That Gazetteer was pull long before and was never scheduled to be released as the big setting pooh-bah.
Perhaps its a revisit of Council of Wyrms
Although I have no desire to play that kind of campaign again.
That was my first guess too, but am I right in remembering there was a comment by Mike Mearls that it was something which had never been done in D&D before?
I think it's funny that there was an entire article about how NOT to pitch stuff to Dungeon/Dragon by saying it has "a twist," but that's how they pitch their products.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.