I finished running Hoard of the Dragon Queen last night. My group will begin Rise of Tiamat next week. Given that Ed Greenwood was writing about Tiamat in 1983 (his tremendously important articles on the Nine Hells) and that Tiamat herself in D&D predates Dragonlance by several years, I've had no problem with the current FR storyline.
Are the adventures FR stories? Yes, yes they are. The fact is that running them in Krynn would feel utterly wrong. Even running them in Greyhawk would feel wrong to me (and most of my home games in the last 20 years have been set there). And the reason that they are Realms stories is because they take advantage of the characters and societies of the Realms.
I've read a lot of adventures that you could set anywhere, including more than a few that are allegedly set in a particular world. I could conceivably set Hoard on another world, but Rise has so many links to the Realms that changing its location would rip out too much for me to consider it worthwhile.
Now, the Temple of Elemental Evil is entirely a Greyhawk thing, with - in particular - the ties to Iuz and Tsuggtmoy and Prince Thrommel cementing its place there. (Although, to be honest, most of the adventure itself is pretty generic). Tharizdun? Originally Greyhawk. Very much so, although his use in the 4E setting was done extremely well. I've nothing against lifting something originally from one setting to use in another as long as it's done well. The Vault of the Drow and Lolth might have started out in Greyhawk, but far more has been done with them in the Forgotten Realms than ever was done in Greyhawk.
And so we get to the Elder Elemental Eye in the Forgotten Realms. Yeah, I'm a bit conflicted about that. (I'm also very much not a fan of conflating Tharizdun and the Elder Elemental God, although I can well see how it happened.) Using Tharizdun in the Realms first occurred during 4E as part of the Abyssal Plague cross-setting storyline, which I pretty much missed as I was not running D&D Encounters at that stage nor reading the novels. The novel is
Sword of the Gods by Bruce Cordell, the adventure is
The Elder Elemental Eye. The adventure is pretty dull, although it has one or two redeeming features.
I *am* a big fan of using the Princes of Elemental Evil, though. They are not a part of the original Temple of Elemental Evil design, and only Imix makes an appearance in Monte Cook's 3E revisit of the temple. (I added one or two more when I ran the temple as part of a 4E conversion last year). I think they're criminally underused, and I'd really like to see them appear in this adventure - or at least get referred to.
Ultimately, I'm in a "wait and see" mode. I'm fine with extra elements being added to the Realms, if they're done well. And I'm far more interested in seeing what the people and factions of the Realms do in response than just thinking "this would be better in Greyhawk".
(Indeed, if we ever see new Greyhawk material, it needs to do a lot more on setting up the personality of the world than has been seen in many Greyhawk adventures...)
Cheers!