given what people are expecting... almost certainly. We're setting ourselves up to be let down
With the level of build-up, I'm expecting something along the lines of a SCAG for Eberron (or whatever the setting is). There's no way we're going to see a setting book in the vein of prior editions, and that's fine. What I will consider a successful product would:
1) Get something on hobby store shelves that actually gives new players enough info to even know they could look at earlier edition material for more info. A foot in the door, essentially.
2) Opens up the DMs Guild for third party publishing. Keith has pretty much said he's got a lot of things that he could write up that wouldn't be profitable enough for WotC to worry about.
3) Is reasonably faithful to previous edition material. There's quite a bit of difference between the 3.5 and 4E books, mechanically, but the flavor is consistent enough.
An online PDF, whether at the Wizards site or DMs Guild wouldn't accomplish #1. There has to be some sort of physical product. My understanding is that the setting announcement plays into the formal release schedule, so I
think we're okay, here. I could be wrong, though.
Really, I don't see any issue with #2. If they're teasing this much for a UA article, they deserve whatever rains down on them. Again, this isn't my understanding of what's being teased.
If they do some sort of "Other Worlds Atlas" book, covering multiple settings, it could go either way on #3 (and, maybe, #1). A SCAG-sized book should be able to give a good enough overview of a setting. I don't see how a book that size could do anything worthwhile with more than one, though. You'd have to leave out
something important, whether that meant all crunch and no fluff, no crunch and all fluff, or an incomplete mishmash of both.
Note: I'm not saying there has to be deep info on the inner workings of the Cults of the Dragon Below, Sarlona, the Dreaming Dark, Xendrik, each of the nations and Dragonmarked houses. SCAG didn't go into Undermountain, Chult, etc. There's a balance. I'd just like to have enough to give a good starting point and compass for anyone who coming to Eberron in 5E. That should be both reasonable and realistic.