Basically I'm just overwriting the, in my humble opinion, apocryphal story events and cosmology changes implemented in 4e FR (Mostly sticking with 3.5 lore, save for some small things from 4e and other things I'm creating from scratch). The pivotal concept of the change being an event called the “Portal Storm”, which caused an abnormally large amount of portals to open and close all over Toril over the course of about a decade or so. This event caused a large amount of planar creatures both sentient and otherwise to be stranded in Faerûn and beyond, and enough time has passed since this event (perhaps a couple centuries or so) to allow these planars on Toril to begin mixing and integrating into the environments and societies of the natives. These beings mostly consisting of aasimars, tieflings, gith, and especially genasi (I've got a thing for them), along with other planars exotic and otherwise that would have the ability to integrate at least somewhat successfully with existing Faerûnian cultures or start their own (I would
greatly appreciate suggestions). Along with other changes such as more solidified nations and fewer independent city-states like those on the Sword Coast, a larger role played by off-planet influences (spelljammers ((D&D spaceships)) would be uncommon, but far from rare), and other things.
As far as races go, most of the new core races are simply going to be either planetouched or something similar, such as dragonborn being descendants of half-dragons, eladrin being elves with fey creatures in their ancestry, deva simply being reflavored as aasimars, genasi being re-split into their much more distict and subdued elemental varieties (as I'm sticking with the 3.5 concept of separate, distinct planes for each element rather then the Elemental Clusterfuck. So fire genasi are just fire genasi and don't have all the overblown energy veins or crystally hair, and the same goes for water, steam, ice, lava, air, and all the other elements), and planetouched such as teiflings having much more subdued indicators of their race rather then the spawn-of-Mephistopheles look they have now (Tiny horns rather then gargantuan ones, no four foot long tails, basically a look that would allow them and any planetouched to at least somewhat pass as human with a lot of disguising and some heavy robes/hoods if needed).
I haven't entirely worked out an exact date or year for the Portal Storm to happen quite yet, maybe I'll have it happen the same year as the events that brought about the 4e changes or something along those lines. I may change the exact cause of the Storm once I get more into it, but at the moment I'm thinking that a powerful villain or cult attempting to open a giant portal to the Far Realm had their extremely powerful spells thwarted by some force (perhaps a group of adventurers), but instead of stopping the spell altogether, it essentially went haywire and began opening small portals to Toril from all over the planescape and took a decade or two for the titanic magic throwing the planes out of whack to finally die down and bring the portals back to their typically rare rate of occurrence. The main antagonists of the campaign I'm working on this for will be this villain or group resurfacing to make another attempt at the spell after hundreds of years of preparation.
Also, I do plan on introducing some elements of beyond extra-planar origin later on in the adventure. Basically the party comes to learn that the Far Realm is a sort of "Border plane", for lack of a better description. Basically the unstable soap film that encircles the bubble that is the planescape. It's the barrier that would mark the border between the universe (planescape) of the Realms and the far-off, other universes that make up the vast multiverse as a whole. The machinations of the group/person trying to reach the Far Realm is somehow able to basically send out ripples past the Far Realm and into other "nearby" universes of the multiverse, ripples that are picked up by beings of a universe that is none too friendly... let's just say that it's a universe run by the employers of our good, old, pal Cthulhu (Mwahahaha!!). Though that crazy sack of bad-ass isn't the point of this thread, I'd like to focus on the setting, as I'm going to be using it in more then just this campaign.
I would greatly appreciate things such as tips, suggestions, pointing out things that I would need to clarify or rework in order to fit in to the redone world, and especially perhaps links to some stuff that may have to do with what I'm doing (I would jump for joy if someone pointed me to somewhere that had 4e character stats for 3.5 style genasi!), any sort of feedback would be monumentally welcome and helpful (Well, other then flaming and such, lol).