My opinions are quite positive!
Overall, this is a pretty big step up from One True Cosmology that Wyatt and Mearls had talked about before. The overall message is one of inclusiveness, and that is fabulous. If the 5e DMG basically includes his closing paragraphs about how cosmologies can be very different beasts, I'll get some warm fuzzies, even if they completely ignore it in their development efforts (and it doesn't seem like they would, given this article...so, awesome!).
I think I can tease out a bit of the disconnect I have when I see Wyatt talking about the problems with having this rich, evocative, multifaceted multiverse of dynamic, interesting otherworlds:
James Wyatt said:
Everyone knows that demons come from the Abyss, right? Well, except they come from the Twelve Hours of Night in the Pharaonic cosmology, and in Eberron they come from a couple of different planes. The Blood War is an important element of D&D, right? Except how does it make sense in Eberron, or in the 4th edition cosmology?
The Blood War isn't an important element of D&D. It's an important element of
Planescape (and possibly by extension
Greyhawk).
Demons coming from the Abyss isn't a D&D trope, it's a
Greyhawk and
Forgotten Realms and
Planescape trope.
D&D is so much bigger than those settings which gave it its shape, and we don't need to be tightly tethered to those legacies (though we certainly should use them as examples of what you can do).
These elements have contexts that are local and specific. The Blood War is important in Planescape because it re-iterates Planescape themes (like the tension between order and chaos and the ambiguity of evil). The Abyss is a little more omnipresent, but it's still ultimately about the settings that employ it. And if you're not playing in PS or in a particularly planar version of GH, why the heck would you even need Bytopia? It's like saying gnomes are from Zilargo, so we need a Zilargo in every D&D game.
In a functional way, all the PC's know is that the demons come from beyond this world, from a place of evil. Call that the Twelve Hours of Night or the Abyss or the Dark Pit or the Elemental Chaos or
whatever. The important thing is that the explanation meshes with the world of your game. If you're playing an Egyptian-themed game, the Abyss doesn't make sense. Since that Egyptian game is D&D, too, D&D doesn't necessarily = a certain origin for demons.
And if you're not playing in Planescape or Greyhawk or Faerun or whatever? Well, lucky you, you get to
pick where demons might come from, if it ever comes up, using it as a way to customize your game. Maybe you pick the Abyss. Maybe you pick the Twelve Hours of Night and marry it with the worship of Asmodeus. Maybe they are spawned from the Nightlands in the north where the taint of evil spreads.
So now the only concern I have is about the tenacity of the default. I'm generally cool with the Great Wheel being kind of what the spells and monsters use for the first release -- if only because D&D has presumed
Greyhawk even if it didn't mean to, in a lot of ways, so it GH has wormed its way into nearly everywhere else. But if they release Eberron 5e and it doesn't have the Orrey, or if they release a Nentir Vale setting for 5e and it doesn't have the World Axis, if they somehow feel the need to cram the Great Wheel into
every corner of everywhere, it'll be a problem. It'll be a little like 2e's "Planescape everywhere!" all over again. And that's not great!
The article allays many of my fears, though. The only remnants are concerns for the future and a hope that they're not going to be monolithic.
And, again, just to emphasize the point,
GREYHAWK/FORGOTTEN REALMS/PLANESCAPE LORE IS NOT D&D LORE, LET US NOT CONFUSE THE TWO!