Been having a few random thoughts, mostly around the elven sundering and how it might have destroyed empires before they began and how that might leave "wreckage" along the sword coast that cannot be explained and only exist because of strong magic that cannot easily be undone by a simple altering of the time stream.
Then i got to thinking about ruathym and i remembered in 4e that a tree was introduced that seemed to be some kind of dimensional anchor and had a simile with a tree that existed in planescape (cant remember if it was called the tree of souls or not).
Now powerful elves could summon arakhora so what if this tree was an arakhora of sorts, but not a regular arakhora because that would be dull and has been done before.
How about the sundering destroyed the empire that summoned the arakhora before they could summon it. The sundering left behind a soul memory of the arakhora, a ghost of sorts. It possesses a tree near to where it once lived and is reborn after a fashion, but of course not exactly the same.
I think i might have a look into all the quotes i can find about ruathym and do a revamp of it at some point. This tree might be a good place to start.
Just to help you look into it, Yggdasil is not 4th e creation - its Norse mythology incorporated into D&D... i think originally back in the deities and demigods book way back when.
Yggdrasil was treated quite extensively in the Planescape line, either (or both - don't have my PDFs in front of me) in Planes of Chaos and/or Planes of Conflict (for 2E).