They'll have a hard time stopping people from smoking at the campsites themselves.... now out in "the open" on the trails is a different thing altogether, they could ban that and it would just be somebody's job (yuck) to go around enforcing it.
What I've noticed around here, just in general, is that places that have *banned* smoking from the property, still haven't/can't do anything about people smoking in their cars in the parking lot. You can tell, 'cause that's where all the smokers hang out now.

We had one lady at work that brought her pick-up with lawn chairs in the back and made quite the lounge! She got alot of the "evil eye" but nobody could quite figure out that she was breaking the rule, exactly.
I would think that's sort of the same problem as at a campsite. If you're smoking
in your RV, or really if standing in the doorway, whatever, they'd have a really difficult time stopping that from happening. That's about as far as they could take it, and it would be really hard to enforce even then.
Having said that, both of us smoke. I don't smoke as much as my husband so it doesn't really bother me to go 4-5 hours, him that's an issue. I was doing the preliminary research into the WDW hotels when the new smoking policy went into effect. When I said something, my husband just said "well that answers that, we're going to be camping". So, hey, if we're in the least bit "typical", you're going to find soon enough that every smoker that wants to stay on property is going to be headed to the Fort.