No matter how they do it, someone will be mad.
I think Ravenloft was a let down because of the page count and the trimmed down nature of it being a single hardback.
Most of these deserve a lot more than decades of lore, factions, NPCs, and monsters crammed into 256 pages.
To do them right, the settings should be at least three books, if not four. A box or slipcase with 3-4 books and a heap of accessories would be best.
The first book is the main setting info. History, lore, manor cities, regions, character stuff, new rules, etc. Really go in depth.
The second book is nothing but monsters. Creatures, beasts, factions, enemies, legendary creatures, and other NPCs. But done properly. With ecology, tactics, lore DCs, interesting actions and defenses, etc. Basically the best parts of how earlier editions handled monsters.
The third book should be an adventure path that takes the PCs from 0-20. Yes, zero. And moves them through the high points of the setting. Having played through the AP should give the player the chance to learn the high-level lore from the setting book and a lot of the details along the way.
The optional fourth book should be an anthology of shorter adventures and side quests that can be added to the main AP, dropped in to any campaign in the setting, or maybe used somewhere else. The focus should be on filling in the rest of the lore blanks rather than compatibility with or ability to port them into other settings.
Though another thought is to go Enemy Within and do a massive, sprawling, 5-6-part AP that covers it all. Though I don’t think they (or we) could handle how awesome that would be.