Why would a company want to ban employees who eat unhealthful food? Presumably, there would be some benefit in lower health care costs, but these would likely be far outweighed by the additional costs the company would incur by reducing its potential labor supply. Thus, it's highly unlikely that any company would attempt such a thing, and if it did, it would probably be at a competitive disadvantage and eventually fail.
Similarly, a company can make a cost-benefit analysis about smoking. Scotts decided that it would probably gain more by banning smoking that it would lose by limiting its labor supply, but it remains to be seen whether this will be true. If not, Scotts will likely realize that the policy is costing it money, and rescind it. If is beneficial, some other companies may emulate it, while most will probably impose a more sensible policy such as requiring smokers to pay slightly higher health insurance costs. Either way, there is no way smokers will become unemployable.
The courts are now going to have to keep this in check. It it smoking at home today, it is burgers and french fries tomorrow....because you will be costing the company money!