I have the vague feeling that I've seen this done before but can't recall much detail, so I'm going to call it mostly my independent idea. Point me to yours if you've done it before though!
The idea is to reinterpret the planes rom the point of view of someone who shifts the Good-Evil and Law-Chaos axes one space over, and regards what we consider the interstitial planes as the poles.
Shift clockwise, and you get the following:
The Beastlands are "pure good" because they're Eden, the plane of unspoilt nature. It's the prelapsarian world, Creation without the Fall, so it's untouched by Evil. Arcadia is the Lawful Neutral plane of perfectly ordered societies. Nemausus fell because the Harmonium's camps touched the plane with evil. Between them is Bytopia, the plane where people exist in a fallen world but work diligently for the good of themselves and others. The message is that with effort, with deeds, with striving, you can be perfected.
Here the interstitials are Elysium, which is the stillness of the eternal Love that exists even in Creation, beckoning toward perfect sinlessness, and Mount Celestia, the plane of the righteous struggle (jihad in its proper definition), Law-most outpost of the Upper Planes.
Archeron is Lawful Evil, the plane of order by force and terror, the home of orcs and goblins. Gehenna is the finite plane of ultimate evil, home to the General of Gehenna, naturally. It speaks of the ultimate self-contained nature of evil, says this view of the planes. Baator is the attempt of the fallen angels to duplicate the perfection of evil, the Hell that rebellion can create. Mechanus is merely the evil of the uncaring. The gears grind on, regardless, not actively evil, just grinding.
On the Chaos side, it's Pandemonium that is perfect chaos. Limbo is merely formlessness; it is potential, source, a proper part of Creation. Pandemonium is madness with mind, pure unreason. The mix of chaos and evil is Carceri, where irrational evil (like the selfish Titans, predating logic but sentient enough to be greedy) is locked away from the rest of the Universe in the Eternal Prison.
The interstitials down here are the Gray Waste -- the final stop for anything that can't hack the purity of Evil, which is most souls that attempt it -- and the Abyss, a crack in creation that doesn't make sense, which should be contained in Carceri but isn't, as mad as Evil gets.
On the brighter side of Chaos, wild Ysgard with its Yggdrasil and its floating earth and rivers of fire testify to the magnificence of freedom for its bold Norsemen and all those who embrace independence in the name of making a better life. The slightly more-discreet Olympians are still pretty boisterous, but their love of democracy and mathematics puts them as far away from Chaos as you can get when still entwined with human (or elf) society and favoring the pursuit of the passions.
I'll let someone else shift counterclockwise if they like.