Eldraine could share some common elements with Witchlight because they are settings where the feys enjoy more relevance.
I guess maybe it is too soon for a sourcebook about the setting because they have to writte the end of the plot, and to draw the maps. What if later they want to add new characters?
Eldraine could be perfect if we wanted a magic cook or a magic farmer/gardener "class".
The big difference is that back in the day they got a whole year of development for a setting, while now it's about 2/3 the card face content (everything is a large set) but 1/3 the lore (because only one set in the location).
Eldraine is just NOW getting its part 2. And while it has to serve as a "change-it-up" phase 2 of the setting, it also has to fill in the gaps for what they wanted to do in the first set but didn't have space to do. Originally Eldraine was supposed to be 2 sets in 2019-2020 but then they canceled the second one in favor of a return to Theros (partly to help set up Elspeth's role in the Phyrexian Invasion Arc; partly because they wanted to make a Greek sword & sandals style D&D book in 2020 too).
So half the set is fulfilling outstanding phase 1 "core Eldraine" tropes while the other half is showing how they can change up the setting post-Invasion.
So the courts have crumbled in their power but they're still there just in the distant background.
My point with this all is that the coffee table books had a lot to work with. Zendikar and Innistrad each had 2 different blocks to tell the story of, and Ravnica had 3 blocks to tell the story of (and even had a second coffee table book just for the set of War of the Spark, and an entire D&D sourcebook on top of it rather than just a planeshift article). The Dominaria coffee table book had TOO MUCH content to cover all of it so just focused on the Domains and some additional key points about Terisiare and Jamuura -- it's focused on the areas that were in focus in the Dominaria set, when they first tried to do the setting as a cohesive whole rather than picking a location and time period and exploring that in depth. Think a Forgotten Realms Campaign Setting: not a Abeir-Toril Campaign Setting, but specifically on Faerûn, but not zoomed in to the Sword Coast or Chult or Icewind Dale or even into one of the cities like Neverwinter, Waterdeep, or Baldur's Gate, like various 4e and 5e books have done. Kaladesh, Amonkhet, and Ixalan had just a single block a piece when their books came out, but even that was a large set and a small set, while Eldraine until now had just a single large set to draw on.
I'd say that Eldraine now has enough lore content to do a coffee table type book, and thus has enough content for it's own tie-in book. But I don't see that happening as it would have been announced before now. I could definitely see them releasing more digital-only products like this though. And I wouldn't be surprised if we get a pay-for Monstrous Compendium for every Magic: The Gathering release going forward.
Outlaws of Thunder Junction and Bloomburrow seem especially apt for Monstrous Compendiums!