In my own version of the Great Wheel I long ago postulated the existence of "previously hidden" layers of planes like the Heavens, Paradises, and so on, so as to balance out the Wheel perfectly. That is, whenever one plane has less layers than its opposite, in the official cosmology, my version gives the "smaller" plane more layers to make up the difference. Thus, I have 666 layers of Heaven, though the actual mountain that is all most mortals know of the plane ends at the 7th layer (which most of them never even reach, in fact). This also means there are 9 layers of Olympus, 4 layers of the Beastlands, 6 Paradises instead of 2, and so on... the one evil plane to get this treatment is Hades, which has a 4th layer that's sentient and typically eats travellers unfortunate enough to stumble into it.
But then, I wasn't planning on using the "Sidereal at the heart of every layer" explanation in my game either- there can and will be planes without Sidereals at their heart in my game- so for me the issue of balancing Sidereal alignments is moot in any case.
As for the Demiurge "tier" issue, I think they are in fact Eternals, but in a similar manner to how Hero-Deities are gods. They're a transitional step, in other words, not entirely the next higher tier but rapidly (on an Immortal timescale anyway) becoming it. And by this token, I think it's worth asking whether we really want to be giving Hero-Deities a Cosmic ability for every artifact they don't have- won't this end up causing balance issues too, since normally they'd have less than 6 Divine Ranks?
I did strongly prefer the notion that there is only one Demiurge in a particular universe/cosmos, particularly since I am myself familiar with some of the mystical/occult lore that U_K based the notion on in the first place, but Ltheb's story idea is too cool to pass up so my opinion has changed.
Thinking of it in terms of what a Demiurge really represents, compared to other Eternals, perhaps it breaks down like a universe with multiple-personality disorder. I have, in my homebrew, a Goddess of Insanity who is herself insane, and who had alternate personalities of hers "cleave off" into deities in and of themselves. Why couldn't a Universe do the same thing, even if we assume the existence of an actual Demiurge represents the universal consciousness "waking up" from an eons-long slumber?
But then, I wasn't planning on using the "Sidereal at the heart of every layer" explanation in my game either- there can and will be planes without Sidereals at their heart in my game- so for me the issue of balancing Sidereal alignments is moot in any case.

As for the Demiurge "tier" issue, I think they are in fact Eternals, but in a similar manner to how Hero-Deities are gods. They're a transitional step, in other words, not entirely the next higher tier but rapidly (on an Immortal timescale anyway) becoming it. And by this token, I think it's worth asking whether we really want to be giving Hero-Deities a Cosmic ability for every artifact they don't have- won't this end up causing balance issues too, since normally they'd have less than 6 Divine Ranks?
I did strongly prefer the notion that there is only one Demiurge in a particular universe/cosmos, particularly since I am myself familiar with some of the mystical/occult lore that U_K based the notion on in the first place, but Ltheb's story idea is too cool to pass up so my opinion has changed.
