The catch with this is they're doing a big book in November. Which is what Mearls and Crawford have been working on for a year.
Getting another entire book written in just five months will be hard.
There's a reason the spring adventures have been reprints, and why the Perkins didn't work on Tales from the Yawning Portal...
That's why I said that were it to be a gazetteer of the various campaign settings, they'd probably just copy/paste a lot of stuff they had written for those campaign settings previously. I mean, you could pretty much just edit down and re-print the Eberron and Dark Sun 4E books and throw a 5E logo on the front, seeing as how nothing has "changed" in either of those settings in the move to 5E.
Obviously none of us who aren't alpha testers really know what will occur in the spring. But it was merely my guess that because Goodman Games was taking on the role of "adventure reboot" company for 5E, that perhaps that would remove the need/desire for WotC to do a second Yawning Portal-style book themselves. And if they decided not to do adventure re-prints... what other "minimum creation" kind of book could they release that would ultimately support the Autumn 2018 adventure book and game mechanics guide? Thus the idea of editing and re-printing large swathes of the already-published-previously campaign settings as a multiple-setting tome.
We'll find out in about five to six months regardless.