There's been progress, but there's a long way to go.
It is possible to get a smoke-free hotel room/suite pretty easily, but unless you know your hotel tower was built within the last 5 years, it's likely that even the smoke-free rooms will have been retrofitted/renovated, and the most sensitive noses will still twinge a bit. Look for the newer towers at established greats like the Venetian's Palazzo towers.
Since passage of a clean air act in 2006, Vegas has been slowly coming into line – you cannot smoke indoors at the airport anymore, and any bar that serves food, and all restaurants, needs to be smoke-free. The show rooms and theaters are also smoke free (though there may be exceptions here).
The casinos, as far as I can tell, all still allow smoking, from wispy anorexic Capri slims, to fat Cuban stogies (shhh!). I cannot recall ever seeing a pipe smoker, if that's any consolation?
Your best bet for 100% smoke free is a hotel just-off-strip that doesn't have its own Casino.
Personally, I think a single on-Strip hotel going 100% smoke free would be a HUGE selling point and differentiator (kinda like universal free wifi)… But thus far, pretty much no one who owns or operates such establishments seems to agree with me, and it's more likely we'll just see a more natural transition to smoke free as the older generation of visitors dies off from a variety of nicotine-related illnesses.