Upon further thinking , a billion or not, if you are setting it on "earth" in a billion years.
The solution to over-thinking something is not further over-thinking.
You have thrown out a REAL place, and a REAL time frame.
Think of the time frame as metaphoric. "A long, long time from now in, well, here".
I understand there is fantasy in here, and he's going to use soft science/magic. The fact about it though is that I can't imagine any perceivable way that anything could even be remotely familiar to us.
This is obviously not an attempt at rigorous, speculative science fiction. You said it yourself, "there's fantasy here".
(and before anyone says it, elves and dwarves and such are probably not being roleplayed correctly AT ALL in fantasy games simply because we just can't understand them, so we define them by human standards)
This statement is interesting. By what standards are elves and dwarves not being played 'correctly'? They are works of fiction, and as such, they're meant to say something about
us, not some nonexistent reality where they're objectively real and not metaphor/allegory/flights of human fancy.
We understand them fine, after all, we created them.
This is a tricky subject because now you are getting into real life type of things. Just thinking about Warhammer 40k ,Dune, and Star Trek that reference earth it's completely changed or forgotten.
Also interesting. The various forms of science fantasy (and in the case of WH40K and Dune, big time scales) in those settings don't bother you -- what's different about them?
I mean, if everything is going to be completely different anyway why set it on earth?
Because the prospective audience is from Earth.
Why not in a completely different universe ?
Because "Earth" resonates more than "some world in the Lesser Magellenic Cloud" or "that place where Mr. Mxyzptlk comes from".
What exactly about earth is it that makes him want to center the game there?
We live here. This one's not rocket science.
Nothing that we will recognize as earth from our era will exist, so why earth?
It still has sentimental value.
The only way this could happen is if we start time travelling. Which is fine if he's going soft science/magic...
If?
Could it be you simply don't like the Dying Earth subgenre? Though, even if you don't, I have to recommend Gene Wolfe's Book of the New Sun. Every SF/F fan should read it, IMNSHO.