The bearer wouldn't exactly have the power thrust upon them. This particular person would have spent his life up until that point training and willing to accept the responsibility of the seed. Also, I can nix the dimensions thing. It really only existed to better tie into Norse mythology. The world tree could simply just be a tree with roots that caress and manage the entirety of the one world it's on.

Highly unlikely that would change your mind, and that's fine. I just wanted to explain that detail.