People have told me that this means that the "new gold floor" will be 25 cents per 1 million gold, but this would mean that the MINIMUM stack size of gold/listing has been increased.
Even if the raised minimum were correct (it is not, as far as I can tell), extrapolating an effective floor in gold exchange requires the synthesis of more factors than that. Whomever made that estimation is just blowing smoke up your ass.
Last I checked gold is about $1.11 per million. That was yesterday though so who knows. As far as I can tell that's pretty much in competition with gold selling sites though some of those go lower. You sell it in stacks of 1,000,000 now instead of 100,000
At least Blizzard has finally given people a viable option to not using gold sellers.