Maybe? I think Eberron works better as something for the D&D fan that's getting bored with the core stuff and want something a little different without getting too crazy.Would you be willing to place Eberron in the Core Rules ala Golarion and have every supplement reference Eberron to get all that?
I would not expect everyone to buy a book every month. Not every book is for every player. But I think a publishing schedule of a book a month would be fine, because that would allow for some more variety in the schedule. So you could get 2-3 Eberron books, 2-3 FR books, 2-3 adventures, a rules option book along the lines of Xanathar's and/or a monster book, 1-2 one-and-done settings, and maybe a book expanding the rules on some topic (psionics, martial adepts, nautical adventures, etc). This is something that could almost certainly be done profitably, but it probably wouldn't be the path for maximizing ROI.I can barely do a book a year. A book a month? I would stop paying attention to anything WoTC is selling, because I just couldn't afford it.
2-3 supported settings, with one-and-dones sprinkled as needed/desired.And I'm not sure I would want to have only two to three settings, because we have a fairly good idea of exactly what that short list would look like.
The psionics book would probably work best as a generic psionics book, but designed with an eye toward how psionics operate in Eberron. Basically, making sure the rules fit the world where they're most likely to see use.I love Eberron as a setting, but that sounds like far too much. Breadth of humanoids? The vast majority of humanoids are covered very very well, you could slide the few that aren't into a different book. A psionic specific book? Don't see the appeal. It might work as a generic psionics book, but that will barely sell, and Eberron specific psionics? I don't think there is even a niche for that.
As for the humanoids, I'm thinking an exploration of the various humanoid cultures in Eberron, along with stat blocks for various roles. Orcs, for example, have three distinct cultures: Shadow Marches (with their tensions between pro- and anti-aberrant factions), the Demon Wastes and their age-old devotion to the Flame that Binds, and the more classic orcs in the Mror Holds. Plus the House Tharashk offshoot from the Shadow Marches culture. Get in a bit on what makes each of these tick, and provide some stat blocks for representatives of each culture (Shadow Marches could have hunter, chief, druid, and aberrant cultist, for example). Then do a similar thing for goblinoids, exploring both the nascent nation of Darguun and the lot of goblins in the Five Nations. Go into some detail on Droaam, the factions operating there, and the Daughters of Sora Kell. Some of that stuff might work better in sourcebooks covering the locations instead of peoples, but still.