Well Realms & Worlds teased a plot hook for Thay.
I suspect we will get a reasonable run down and some plot hooks for most nations in FR.
Remember that Red Wizards of Thay is a faction as well so I would not be surprised if Thay got the 4 pages, or at least 2 pages, perhaps including the faction material, perhaps not, but Thay is one of the biggest villians and draws of the whole setting.
I think the average will be anywhere from half a page, to several pages. Really depends on how large the book is, although the article also confirmed the books are large, not just "full sized" which is vaguer then large. I'm thinking minimum 256 (size of Waterdeep: Dragonheist), most likely 320 pages (the size of the 2014 PHB & the size of the Forgotten Realms Campaign Setting 3e book from 2001), or hopefully 384 pages (the size of the 2024 PHB) if it's this big it's very likely even Kara Tur & Zakhara get some coverage.
Also remember the FRCS had a big gazetteer section on the Dalelands, which is now in the FRAG not in the FRPG, which free up page out for other regions.