Mercule
Adventurer
To clarify, I think you're right about being able to shift the Eberron timeline to capture an urban feel. It would probably end up feeling a lot like the world of Incarnations of Immortality. While I enjoyed those books, I don't think it's a setting that would hold my interest for very long. Using Eberron for it, well, a sledgehammer is a hammer, but you won't get great results to use it for hanging a picture anchor.
Unlike Greyhawk, Eberron actually does have some unique rules. At the very least, there are rules options that are missing from the game (the one UA article didn't really please any existing fans, AFAIK). I think there's a good case for at least doing a SCAG-like book for Eberron/Khorvaire just for that reason.
As for Greyhawk, I think the only real argument for publishing a 5E sourcebook is that there hasn't been anything more than a gazetteer done since 1E. Next year will be 35 years since the red-and-gold box was published. That's probably far enough back that you could practically reprint 80% of the text, update the graphics and a few stats, and have your SCAG book ready to go. Heck, just drop any stat blocks for rulers (quite a few, IIRC) and you might not have anything mechanical to change. Boom! Evergreen source book. For 6E, just order a new cover and change any logo-type graphics and you're good for another print run.
Unlike Greyhawk, Eberron actually does have some unique rules. At the very least, there are rules options that are missing from the game (the one UA article didn't really please any existing fans, AFAIK). I think there's a good case for at least doing a SCAG-like book for Eberron/Khorvaire just for that reason.
As for Greyhawk, I think the only real argument for publishing a 5E sourcebook is that there hasn't been anything more than a gazetteer done since 1E. Next year will be 35 years since the red-and-gold box was published. That's probably far enough back that you could practically reprint 80% of the text, update the graphics and a few stats, and have your SCAG book ready to go. Heck, just drop any stat blocks for rulers (quite a few, IIRC) and you might not have anything mechanical to change. Boom! Evergreen source book. For 6E, just order a new cover and change any logo-type graphics and you're good for another print run.