This went live on US servers after today's maintenance. Blizzard's price is currently set at a minimum of 0.25 per 100,000, so gold will sell for no less than $2.50 per million. Third party gold will have to remain cheaper, but I wouldn't be surprised if prices increase at least a little.
What remains to be seen is what impact this will have on third party gold sales, and what percentage of gold buyers will actually be willing to pay the higher premium.