OK, RDM confirmed in his podcast he never really conceived the show being in the future. But he definitely wanted to keep was the Thirteenth Tribe’s exodus and the trail of clues left by the Thirteenth Tribe.
Given how in the ending, he went to great lengths to make this all work scientifically, hinting that this desire didn’t suddenly spring upon him when writing the finale (some say he went too far), I can’t concieve he ever intended for there to be an extinct civilization in our past over 152,000 years ago, especially since he seems to think nukes can sterilize a planet (they can’t). So the decision to set the show in the past seems to have come first. What came after, do you think, and in what order:
-the fact that the Thirteenth Tribe settled a planet that they called Earth that wasn’t our own? Was there ever a time when he imagined that they did indeed settle our Earth?
-the fact that the two Earths had nothing to do with each other?
I think part of it is also that there was a danger that if the Writer’s Strike went on too long, there was a danger the show wouldn’t come back, so there’s also the fact that he had to provide an ending. Had they not been able to film 4.5 I guess we would have been left to assume that the show takes place in the future and that this is the real Future Earth. Really, the whole thing with the tomb of Athena doesn’t work for another planet (Kevin Grazier, the science advisor, said as much).