Look what I just found today:
New and Outrageous Taxes - WalletPop "Sin" Taxes
So-called "sin" taxes are on the hit list for many state and local governments, raising taxes on everything from cigarettes to alcohol.
New York is even toying with an 18% tax on non-diet soda, dubbed an "obesity tax," capable of raising $400 million a year. If the governor of Wisconsin has his way, cigarette taxes will go up 75 cents a pack! The increase will generate $300 million for the state over two years. In Massachusetts, the governor is considering a new 5 percent sales tax on beer. This and other "wellness" taxes could cost taxpayers as much as $150 million each year!
So if they call it an "obesity tax" - they are only going to tax non-diet soda, sounds like the hardest thing to regulate. Especially at places that let their customers fill their own cups. People will order a large soda & go chose which ever they want.