I'm totally working off of hear-say here, but I don't think that's quite it.
It may be an entire new world, but the setting itself will be more localized (and thus better able to be dropped into any other setting). I heard it would be some sort of city myself.
As for being an undead Savage Species, it might be, but the way I heard it was that the "ghosts" wouldn't be the undead kind we're familiar with. I also heard they would (aside from living characters, which would work in the setting also) be the only kind of "variant" character type available, with no other undead creatures available (basically, itd be a city of the dead, not the undead).
Again, I'm working from half-rumors and such, so don't take any of the above as gospel. I could be dead wrong (pun intended - sorry!).
I think the idea though has quite a bit of merit. I mean, adventuring on after death, its rather innovative as far as D&D goes. Usually PC death is the end of the character, or you just fast-forward to the Resurrection spell. Planescape touched on this idea a little bit, but not much. I'm pretty jazzed to see more of the idea. I can just see the subtitle now... "Death is only the next great adventure."