I'm in the midst of retooling my campaign for 4e, and one of the big things I'm working on is the religions of my homebrew campaign setting. For 3.X ed., I just had 4 generic philosophies (Light, Darkness, Nature, Knowledge) that the PCs chose to follow (or had to follow, in the case of divine spellcasting classes).
I've decided to expand it a bit & actually create deities (but still working with the philosophy idea—it'd be sorta like the option of pantheon worship in Eberron). I'm also trying to work with the new cosmology a bit—IMC, I just had the Celestial Realm (with all of the LG, NG, CG, LN, and some N outsiders there) and the Infernal Realm (with all of the CN, LE, NE, CE, and some N outsiders there). Working with the new cosmology, I'm sorta thinking of having the fall of one of the islands in the Astral Sea into the Elemental Chaos be the cause/creation of the Infernal Realm in the heart of the Elemental Chaos.
Currently I'm kicking around the idea that, IMC, Ur, the god of darkness and chaos was the one to kick off the conflict between gods & primordials (twisting and corrupting the primordials to chaos and evil in order to gain allies for his war against the gods), and that Ur is responsible for the creation of demons & devils. Proximity to Ur determines the degree of evil shown—Chaotic evil for those nearby, and just Evil for those not as close by (thus devils would be found in the upper reaches of the Infernal Realms, and demons would be in the lower reaches, closer to Ur). Ur's corrupting presence affected primordials as well, creating the likes of Orcus and whatnot (perhaps even corrupting the archons).
Then again, along the same lines, I like the idea of purified primordials, ones who became benevolent and good through the presence of An, the god of light and order (Ur's opposite #). They don't necessarily have to be Lawful Good, but at least non-malignant (representing the benevolent aspects of the elements rather than just solely the destructive aspects). Sorta-kinda like the Titans who were aligned with the Olympians and kept out of Tartarus.
The thing I'm really trying to determine is how primal-powered PCs will operate. From what's said here, it doesn't sould like the primal PC will need to choose a primordial patron and match its alignment (ala divine-powered PCs and the gods). The mention of the primordials in FR has me wondering, though—perhaps the shaman may be a primal-powered version of a cleric, including having to select a patron primordial.