Hinduism tbh.
And Plato

although the former was there first, he got to the idea on his very own.
And I'm sure others had before him, he just wrote it down, it's said early Sumerian writings include reincarnation etc.
On the tutorial level: I guess there's a point there. I actually believe the voice is already there, DavidM said that earlier in another thread (a while back).
Anyway, this is still a great idea imo, although it shouldn't be mandatory!
And I bet there can at least be one GS server currently out of date downgraded to a n00b-server :\
Why not?
The only thing really important imo is that there should be the very same set of physics.
People often have the tendency to change things around for people new, but they should get used to the game quickly.
Then again, I'm sure TeamVortex will be able to figure that out by themselves just fine (as DavidM has expressed his opinion on dynamic physics many times before).
The only thing that should seperate a newb-server from a regular server should be the players.
However, this brings what might be the biggest problem:
Pros joining newb servers and taking the whole point (and the fun for them) out.
Hence I suggest just this tiny little thing:
In Settings > Player there's should be an option:
Click that and the Deathball tab will be grayed out and the New to Deathball tab should be available (to state there's actually explicitly another tab!)