The only acceptable change to Eberron would be to change the default time in the setting. I wouldn't mind if the default was right smack dab in the middle of the war. Then again, great for War, poor for adventuring.
Maybe right before the war would work. But then you'd basically have what you have now, except less Warforged and less Mournland.
How about Random Baddie X succeeded in doing Y with Khyber and now the entire world is Mournland like?
But then you have a magical Dark Sun.
...
Eberron really has no where to go, does it?
So... fix it up. Make it pretty. Update with popular NPCs. Include a big poster map (but not one that tears out of the book, for goodness' sake).
Maybe right before the war would work. But then you'd basically have what you have now, except less Warforged and less Mournland.

How about Random Baddie X succeeded in doing Y with Khyber and now the entire world is Mournland like?
But then you have a magical Dark Sun.
...
Eberron really has no where to go, does it?

So... fix it up. Make it pretty. Update with popular NPCs. Include a big poster map (but not one that tears out of the book, for goodness' sake).