Hey all!
Tried to post last night, but ENWorld is a bit temperamental lately.
Okay looking at the results:
Fictional/Atlantean = 15
Greek = 14
Japanese = 14
Egyptian = 13
Canaanite = 12
Mesopotamian = 12
Norse = 12
Chinese = 11
Slavic = 11
Persian = 10
Aztec = 9
Hindu = 9
Celtic = 8
N. American = 8
Oceanic = 8
Finnish = 7
African = 6
Lesser Known/Australian = 5
Incan = 4
While fictional (and presumably Atlantean) is top, I think it would be better to set out the first volume or two with established Pantheons/Mythologies.
Between Greek and Japanese I must admit I am a lot more confident (at this juncture) with Greek mythology.
I have also been thinking that if any Pantheon/Mythology has an obvious 'spin-off' or parallel mythos (Greek-Roman, Celtic-Welsh, Aztec-Mayan, Norse-Teutonic, Sumerian-Babylonian, Hindu-Tibetan etc.) That it would also be covered in any such book.
Interestingly, I have been brainstorming for (among other things) the adventure and the first one will probably have an Egyptian theme in it to the extent that quite a large chunk of what would comprise an Egyptian pantheon book will probably be detailed.
So the first Immortals Index will probably be the Greek and Roman Gods. Its high on the list, well known to me, has some great monsters and is generally the defacto mythology when talking about mythology - so it will establish a good base. Of course the flipside to that is that the mythology is so familiar there is little surprise in it anymore...but hopefully I can change all that.
Not sure what the second volume will be, but I'll do a bit more reading up on Japanese mythology and see how I like it.
I'm getting my new computer (a laptop) at the end of this week and then I'll start typing up my notes and see how easy 4E really is to design for. I'd still love to do an 'old school' Deities & Demigods type book with multiple mythologies in it. Though I think the trade off is always going to be the level of detail you give each immortal. As we can see from Orcus entry in the Monster Manual, even a basic treatment takes a few pages. In a multiple mythos book, elements like Aspects, Exarchs and High Priests might only be mentioned (with intended levels) and not detailed.