The Wayfinder’s Guide to Eberron (WGtE) was originally released on DMsGuild as a PDF (and on D&D Beyond) in July 2018. (See also this Q&A: What is "Wayfinder's Guide to Eberron"?) The various parts already included in it (races, dragonmarks, magic items) then went through the Unearthed Arcana public playtest process, as did the artificer class.
Eventually, the final versions of this material were published in Eberron: Rising from the Last War (E:RftLW) in November 2019. At that point, WGtE was updated to include the final versions (as they appear in E:RftLW) of the content that was already in it; the official artificer class was added to WGtE as well, though with only 1 of the 3 subclasses that appeared in E:RftLW (the Alchemist).
As of the release of Eberron: Rising from the Last War, it seems like there’s almost no reason to buy the Wayfinder’s Guide to Eberron. Almost every single character option and magic item that exists in WGtE seems to have been reprinted in E:RftLW, and then the latter adds several additional things that are not in WGtE at all: the Artillerist and Battle Smith subclasses for artificer, reprints of bugbears/goblins/hobgoblins, a "new" orc race (though mechanically almost identical to the existing one in Volo’s Guide to Monsters), a group patrons mechanic, seemingly more in-depth lore, a short sample adventure, several additional magic items, and plenty of new monsters/NPCs.
By the way, this stands in stark contrast to Mike Mearls’ claims back when WGtE first came out that any future print product would be complementary, rather than just superseding/replacing WGtE entirely (even if E:RftLW was only a hypothetical at that point):
This book and a theoretical print release will be designed to complement each other, though some material (artificer, races) will be duplicated.
If we do an Eberron print product, we will design it to complement as much as possible what the PDF presents.
Some things, like the artificer, races, and basic world info, will be picked up for a print book, but we want fans to be happy owning both.
yes, but we will build a print product so that the two complement each other.
However, in responding to someone’s question on /r/dndnext on Reddit about which of the 2 books would be a better purchase (to which the answer was obvious), I did begin to wonder what official material appeared exclusively in Wayfinder’s Guide to Eberron. The only 2 things I’m aware of are listed in my reply to the linked comment, but I was curious whether there was anything else I’d missed. (I’m intentionally choosing not to state which things I identified in my question, so that answers will contain a complete list of WGtE-exclusive material rather than excluding those two.)
What material currently appears only in the Wayfinder’s Guide to Eberron (the latest version, as of November 2019), that wasn’t also reprinted in Eberron: Rising from the Last War?
I’m mainly interested in a summary/list mechanical stuff – e.g. character options, magic items, monsters, etc. – but if there are significant lore elements mentioned only in WGtE and not in E:RftLW, it’d be nice to get a brief summary of what lore is exclusive to WGtE as well. (You don’t need to provide a full rundown of what that WGtE-exclusive lore is – just list the names of topics/sections that only WGtE has lore about, or point out where in WGtE I can find it.) I might count maps and other resources too, if they’re exclusive to WGtE.
Basically, I’m curious about any WGtE-only content that a person couldn’t get simply by buying E:RftLW.