So it seems like the Night Elf souls will be obliterated to build this new seed...
https://youtu.be/YMGN9pK5ZC4
But we won't even know what the seed does. The Forsaken got a long questline to repair Tirisfal and Undercity while the Night Elves just got this seed.. at the cost of all the night elf souls that were killed and tortured.
Even if we got a new world tree out of it which is extremely unlikely, it's extremely bad that the Night Elf souls are being destroyed for it. Instead they should've been part of the actual renewal instead of sacrificing themselves for something that might even turn out to nothing.
I also wouldn't be surprised if the seed gets destroyed given Blizzard's hateful writing for Night Elves.