Despite my bile, I actually do have faith that Wizards is going to see their multiverse promises through. I just wish they'd do something -- anything -- that actually reflects those intentions. Because every time one of these products comes out that is clearly inspired by a classic, neglected D&D setting but /once again/ set on the Sword Coast, I start to think that the big reveal at Gen Con 2015 will be that there's a suburb of Waterdeep called Multiverse.
The core books clearly show the default setting of the new game is that there is no default setting. The classic D&D cosmology (the "multiverse") is assumed, and shout-outs to most of the classic settings are riddled throughout the three books. It's also clear that the Forgotten Realms setting is the first among equals, not due to quality or "worth" but simply popularity.
Publishing most of their adventures and sourcebooks for the Realms doesn't change any of that. If we never see a Greyhawk or Mystara book, that still doesn't change any of the above. The older non-Realms settings aren't being "neglected" as if it were some sort of insult to fans, they just aren't receiving the spotlight because it doesn't really make sense for them to do so.
If WotC wants to publish an adventure that is fairly generic high fantasy, even if inspired by an older storyline, it makes the most sense to put it into the Forgotten Realms. There just aren't enough fans left of Greyhawk, Mystara, and Dragonlance to do it any other way.
Now if they come up with a storyline that pushes the boundaries of the D&D core, it makes perfect sense to use a setting (brand-new or existing like Dark Sun) that incorporates the unique ideas. Dark Sun and Eberron are good candidates for this, as would an entirely new setting.
Doesn't mean we will never see a Greyhawk, Mystara, or Dragonlance RPG book in the future. But I won't be holding my breath, and I won't cry if it never comes to pass. And I LOOOOOOVVVEEE Mystara. These types of projects would be perfect for Kickstarter, although I doubt WotC would use crowd-funding to bring back the classic settings (too corporate).
D&D4 broke its covenant by revealing that Nerath wasn't a unifying setting at all, it was just a holding pen for the stuff the developers didn't care about elaborating (i.e., everything that wasn't Forgotten Realms, Eberron, or Dark Sun). When I see "a" Temple of Elemental Evil set on the Sword Coast I get the same vibe -- someone doesn't care.
If I'm irritated I am irritated because Wizards' words and deeds describe different courses of action, one respectful of that symbology and one disrespectful. I'm not saying they've betrayed us, just that I'd like some assurance that they understand the symbology and that when they visit the crash site in the Barrier Peaks, or the Tower of High Sorcery at Wayreth, or Kalak's ziggurat, or the Mournlands, they're not a day's journey outside Luskan.
No one at WotC broke any covenants or promises, and to say that the D&D team doesn't "care" is very silly. Everyone who has ever been on the D&D design team is a D&D fan who landed the most awesomest job ever, to work on D&D. All of them "care". They (both the individual designers and the teams) don't necessarily have the same opinions and priorities as SOME gamers, but to say that they don't care is just taking things waaaay to far.
There is no disrespect, no betrayal, no disconnect between words and deeds. It's just fans that care just a bit too much about the niggling minutae of "canon" and that read incorrectly between-the-lines on marketing and tweets and just about every communication from WotC.
I'm not saying fans shouldn't care or shouldn't be passionate. Or shouldn't have a favorite setting and hope beyond hope their setting gets an awesome new treatment. I'm hoping for a giant, full-color, detailed treatment of the Mystara setting! But to get upset over perceived (but unreal) disrespect and neglect is just beyond silly . . . all IMO, of course.