Another general comment/response about what is/isn't definingly "Greyhawk" in games:
Since I tend to think of the various campaigns I've run in the Greyhawk setting as parallel timelines or alternate Prime Material plane Oerths---each distinct from one another, but united in their essential Greyhawkness---consequently, I don't worry too much about what "Greyhawk" is or means in the big picture, with respect to that particular campaign. I like variety in my campaigns, since there's so much breadth and depth within Greyhawk to play with, and certianly some of that vibrancy comes from new authors/new ideas entering the setting, as well as my own preferences, and what the players bring to the table too.
When I get around to running my "Land of Black Ice Blight" campaign, that'll be one where Black Ice glaciation has spread south, deep into the central lands of The Flanaess. I might run that set in 576 CY, or 176 CY, or -666 CY. No idea. But that campaign won't necessarily have any bearing on how I want to run Greyhawk the next time around (or, it may, depending on who's playing and how the campaign turned out).
So for me, new/cool Greyhawk material has to pass the sniff test or I ignore it (I ignore lots of other cool, neat Greyhawk material in the course of any given campaign if it doesn't end up fitting in either, of course). If I had a game that required tieflings (an Unseeling Court game inspired by
@Sepulchrave II 's Afqithan demi-plane, for example), they would be a part of that campaign, same for dragonborn or Qualinesti elves or whatever. That doesn't mean that they're on or off the table in the next campaign though. I take each campaign on its own merits, I suppose.
Anyway, I'm off to bed! =)
Allan.