doctorbadwolf
Heretic of The Seventh Circle
I'd expect anything related to the settings to be low priority for them. Unless they can figure out a way to present the material in some way that is more useful to a wide audience.
They must realize that the surveys are mostly completed by more long time and/or diehard fans. So yeah, the demand per the survey might be high, but will people buy a Dark Sun or Ebberon book in numbers like the sales of other books so far? Probably not.
Using the DMGuild as a means of releasing such material seems like a decent idea, but they haven't really done that for anything other than the AL stuff so far. For whatever reason, they seem reluctant to release things that way.
I wouldn't mind some setting based info myself, but I prefer it to come packaged with something else, along the lines of Curse of Strahd and Ravenloft. I love Planescape and Dark Sun, and I'm using both in my current campaign. If they put material out for either, I'd probably pick it up...but until then, I'm managing with what I have already and homebrewing the rest. WotC probably realizes that as well; so much material already exists for these settings that it's tough to come up with something new that doesn't seem like a rehash except with 5E mechanics.
Eberron is interesting/engaging enough on its own merits that a storyline is all that would be needed to get newer players into it enough to buy a book for it.
That said, a world building book with info and options for the major settings would be a pretty good bet. Especially if it came after a story line each for at least two of the settings detailed therein, and included some optional Rules stuff like Dragonmarks as a layer outside of what is there already (I don't dig the feat approach. Even Keith has suggested it isn't how he'd have done it had he had full control.), Action/Hero points, whatever weirdness Dark Sun needs, and a couple new classes, like Artificer and Mystic.
Such a book would pretty much much have to also have new feats, subclasses, races, monsters, spells, items mundane and magical, and could easily have alternate/optional rules for skills. Perhaps also rules for organizations, strongholds, airships and spelljammers, and some guidance on worldbuilding, using various DnD settings as examples.