Here's a thought-
The Great Wheel is mostly, or at least quasi-based on Western culture, with a few outposts from the East.
But that's the side of the wheel we know. If you traveled deep into the ground of the Outlands, perhaps you might eventually come out the Other Side- one based on an Eastern view of the Planes, with a few Western outposts.
What would the Plains be like from here, I wonder?
The Great Wheel is mostly, or at least quasi-based on Western culture, with a few outposts from the East.
But that's the side of the wheel we know. If you traveled deep into the ground of the Outlands, perhaps you might eventually come out the Other Side- one based on an Eastern view of the Planes, with a few Western outposts.
What would the Plains be like from here, I wonder?
I just think the East is treated like most of the other real world mythologies (although Asia has gotten a much more reductive treatment without question). It's relegated to a pantheon that is associated with a plane, much like the Norse and Greek gods. While arguably the rest of the planes are Chritistian European in tone, it's most just derivitive rather than explicitly copied. If you were to expand upon Eastern mythology, I would just drop different pantheons somewhere inside the existing cosmology. After all, there is plenty of room.
Personaly, what I would do would be something akin to how Mount Olympus and the World Tree work. Give a couple asian pantheon's their due, with some significance in planar cosmology and a corresponding planespanning feature that adds new planar pathways. I am not intimate enough with Hindu mythology to throw anything out there, and Chinese mythology already has its writeup, so I can't personally think of anything to add offhand, but there is a very deep well to draw from. I can't think of any good reason why you can't just plop it down in the middle of the Great Wheel (And perhaps even add a few innter planes while you are at it to reflect Wu Xing and the like). If you handle it any other way, it almost feels like saying the two world view are so different as to be incompatible, or diametrically opposed. In a place as large as the planes, why give asian mythology that kind of treatment?
Well they never really officially said where Kun Lun and all the magical mountains in Chinese mythology are (though one of them probably would be Celestia).
And they never really tried to explain on which planes the Nine Worlds/Lokas of Hindu Mythology are.
The concept of the wheel of life goes back to the Greeks and the development of astrology, but the wheel of Good and Evil was developed by Zorothustra and it has basic structural features as the Ying - Yang dualism.
The Palace of Judgement of the Celestial Bureaucracy is on the Outlands but it's a waystation where the dead worshipers of this pantheon are judged and then sent onwards to the correct location for their actions. Non-dead and those outside of the worshiper base may use these portals for a fee for regular travel of trade. I think that pretty solidly implies that the domains of the pantheon are all over the place. Then there's all the Hindu gods throughout Acheron (that is where raksasha originate after all) and beyond. As far as I can tell in looking - Asian myth is not absent from the planes - it just seems like it's under emphasized in many games.
Buddhist cosmology actually involves the concept of multiple worlds, both multiple material worlds and multiple heavens; the heavens each oversee a number of material worlds, and higher heavens oversee multiple heavens. Persons who advance far enough in enlightenment are reborn into higher worlds, and the highest worlds are reserved for those who will no longer be reborn into lower worlds and are shortly to achieve Nirvana.
Relevant to Planescape is that collections of these material worlds surround an enormous mountain, Mt. Sumeru, from which they are all accessible. A Buddhist version of Planescape might have a city on the slopes of Mt. Sumeru accessing various Material planes through gates on the side of the mountain, various hells by walking downwards into the mists below, and various paradises by flight into the clouds above the mountain.
There would likely be 5 Inner Planes, as Asian systems had five elements with different interactions. Mt. Sumeru is said to be rooted upon enormous regions of rock, water, etc. Here you have to break the Buddhist cosmology, since there are only three of these and they're arranged linearly. One might access them by tunneling in to Mt. Sumeru.
While the planes were certainly created as they are by the writers with certain Western-based inspirations in mind, its clearly stated in planescape that the PLanes just are. All mythologies that have another view of what the comsos looks like (and when you get down to it that's pretty much all of them, East, West, North, South, Aborignal and Enlightenment) are either disseminating disinformation to their worshippers (to emphasize their influence) or simply haven't bothered to correct initial missapprenhensions (and of course, the planes do move about, change shape, change name, and so forth over time anyway).
Asian mythologies are explicitly included and referenced in numerous planescape products, their pantheons simply are not concentrated in the way the Norse, Greek, or Egyptian Pantheons tend to be, but considering that they represent larger and more internally diverse cultures demographically anyway, that's to be expected.
Planescape materials do not emphasize Eastern aspects, but neither do they emphasize South American, African, or Slavic-Central Asian cultures, simply because most gamers are comming from a western based fantasy traditions and are asusmed to be from western based prime worlds. This can be easily explained in the following way: unlike the real earth, where the various Asiatic peoples make up a huge chunk of the popualtion that was even greater during the 'medieval' period, the majority of Prime Material worlds are largely western and populations with an different feel are simply of far greater rarity.
One of my players had a japanophile phase once and asked me that very question. After some thought I gave him the following explanation:
1. All the mythologies of our world and thousands of others are present on the planes.
2. We are all from western civilisations.
3. Our planewalkers/characters are played by us.
4. Ergo, our planewalkers come from western/western based cultures.
5. Planes are shaped by belief.
So, the explanation was:
The planes have a very subtle and mostly unknown feature: you tend to end up in places that are somehow compatible to your beliefs. They might be radically different from what your religion told you, but there are still elements that seem familiar. This is because portals you enter etc. are more likely to drop you off at places that are closer to what you expect. Of course, by the very nature of planescape, you never get exactly what you expect, but it means you are much more likely to end up in, let's say the part of Ysgard dominated by the Aesir than by the parts of Ysgard dominated by another cultures "barbarian gods". When visitng the outlands, you will encounter the dwarven mountain ten times for every time you walk by the palace of judgement. And so on.
IIRC, Sumerians had an cosmology which had order and chaos (this culture created Tiamat as a Chaos catastrophe btw) where the ocean was considered the ultimate expression of Chaos, and the King and City expressing order.
So the 4e set is rather similar in outlook to this view.
I thought that Hinduism also had a Great Wheel approach, with reality going along in a wheel, Age after Age, with a different tire, new rims etc to signify the changes from the repetion. But perhaps that's a Western mistranslation.
Well, in the part of Western culture I'm from, we just view things as right/wrong/grey area. We use terms like good, evil, chaotic, and buearcratic (we don't ever say lawful,) but really those are just filters to view what is right and wrong.
I doubt the East is really that different, so I don't think the outer planes should be that different. The inner planes are a completely different story...