On the face of it, it's surprising that landlords wouldn't do this already. The ban is on public smoking, after all, and rented property is private. Landlords already try to ban (or at least severely restrict) pets and children using their properties. (Incidentally, I've recently been house-hunting, and was surprised to find that even condos have no pets and adults-only policies. And you own a condo.) The grounds given, reasonably enough, is that pets and children are more likely to damage the landlord's property. The same could be extended to smokers (ever smelled carpet that's been in a smoker's house for over a decade?).
However, trying to ban smokers seems like a strategy that could only work in a tight rental market. If there's more than enough spaces for renters, then any given landlord can't afford to be terribly choosey. (But could insist on a damage deposit to cover the expected costs of removing any smoking damage, as well as charge rent to include at least part of the property's fire insurance.)
What's truly bizarre are the comments in the article about how it's a violation of "human rights" for landlords to refuse to rent to smokers. I might go along with the claim that it's a violation of something for smokers who can't afford to buy a place to have nowhere to live. But, at the end of the day, the landlord owns the property. Why can't they rent to whomever they want?