I love the world Axis--I was excited about the new planar model when I first read about it, and the Manual of the Planes was the 4e supplement that I was (and still am) most excited about. But I still think that grafting Eberron into the world axis model is a big mistake.
See, I like the world axis because it's cool. And I bought the 4e MotP because I thought the world axis was cool (and also because I'm a John Rogers Fanboy*). It gives me cool ideas, and means that I can create cool adventures or cool PCs to play.
I like Eberron because it's cool--gives cool ideas, leads to cool characters and cool adventures... you get the Idea. And I was planning on buying the 4e Ebberon book because eberron is cool. But this change--it makes Ebberon less cool.
See, one of the cool things about Eberron is the fact that its planes aren't attached to some sort of big wheel or whatever. Instead, they're unattached, floating in the astral plane, whizzing around the material plane like demented magical moons.
And like moons, they had tides, effecting the world of Eberron by making it hotter, more evil, more natural, or whatever, depending on the plane in question. And it had permanent manifest zones, like the link to the plane of sky in southern Breland that made possible a mile-tall city to exist.
James Wyatt, in the article mentioned at the beginning of this thread, lists a number of features that the planes share--that they're a place where summoned monsters come from, a place where the dead go when they die, and so forth.
But Eberron is cool because that list doesn't necessarily hold true. Eberron isn't a place where PCs go to the planes to adventure--It's a place where the planes come to them--whether it's the conjunction of the plane of madness that let forth the Daelkyr and their Aberration children to ravage the land millenia during the age of monsters, or the proximity of the plane of battles that helped turn a succession conflict into the hundred-year-long Last War.
When you say that everything has a fixed place in that cosmos, that the astral dominion of Shavarath can never be closer to the world than the feywild that is Thelanis, you've lost some of that coolness.
I think the world axis is a wonderful cosmology, and I have no problem with applying it to settings where it doesn't detract (I've posted elsewhere about how the world axis fits Dark Sun better than the previous cosmology did). I just dislike that WotC is applying it in places where it makes the setting less cool, and worry that they'll make other changes that reduce the coolness of the settings that they publish.
At this point, I'm leaning against buying the 4e ECS--This F4nboy may have to find some other source of Eberron coolness, even if it means going back to 3rd edition (shudder) material.
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*Watch Leverage!