I say that it might be the dominant drug in 500 years only because the farther out we get, the harder it is to predict anything. I’ll equally concede that opium might be the dominant drug in 500 years, or that LSD might be the dominant drug, or that some newly-discovered slime mold may be the dominant drug.
As for pot, though, care for a wager? If, 20 years after pot’s legalization, it’s not the dominant drug, you owe me a bottle of fine cognac; if it is, I owe you an eighth of sticky greenbud.
Daniel