Athas, the desolated world of deserts, obsidian and ecological ruin that is the focus of the Dark Sun campaign setting, is generally portrayed as a prime world nearing the end of its life expectancy.
It's also said to be the distant future of Oerth. When I first heard this, my immediate thought was that it was absurd; After all, I'd read about it in the context of the Planescape setting, where it was described as a Prime world, albeit one that was even more isolated and obscure than most clueless worlds tended to be. I therefore dismissed it as mere fan speculation.
But then it occurred to me: Could it be that there was a time when Dark Sun was the future of Greyhawk, not just in rumour amongst players, but in some officially published material? Canon can be changed at the whim of its creators, after all, and it's not like D&D's designers and developers never wrote any contradictions or errors; Anything is possible.
Therefore, I must ask: Does anyone know the origin of the rumour that the Dark Sun campaign setting lies in the distant future of the other major D&D campaign settings? Was it ever canon? Or is it merely a popular speculation that became so well known as to be indistinguishable from Truth?