DaveMage said:
Remember one of the premises of Eberron: If it exists in D&D, you can find it in Eberron.
Also remember that this is one of the most often misunderstood mantras. It rather means "If something exists in D&D, you can find a place for it in Eberron."
That's more about the flexibility of Eberron, that it can accommodate a wide swath of different ideas. But it doesn't mean you don't have to do some adaption, in the same way the core monsters found their place in Eberron - but without all of their original fluff.
For example, an adventure involving the Feywild would be translated into an adventure involving Thelanis instead, not importing the Feywild wholesale.
If you have tieflings, it doesn't mean they had the Bael Turath empire, it means you will probably find a place for the race, like in the Demon Wasts.
Now take eladrins. They don't need to become a core race, I could say they're a special breed of elves intermingling with the elves of Aerenal, sometimes popping up (perhaps a bit more common in some families), due to the long-term influence of Irian's manifest zone on the Aerenese elves.
This said, I'd really love to see the Ethereal and Shadow Plane in Eberron gone. They're mainly there because of 3E core rules (shadow spells and ethereal effects and ghosts).
And I shudder at the Shadowfell version of the Mournlands.
Cheers, LT.