What resources do you have for sourcing a whole pig? I'm in central North Carolina and pigs of many sizes are readily available. I've seen 40-50lb pigs on small smokers a few times. And of course 150+ lb pigs on large cookers.
I've seen a decent sized pig on a smoker roughly the size of a Rec Tec 680. He had the butcher remove the head and hind shanks to make sure it would fit.
As for whether or not it's worth it, I think it absolutely is worth it. Maybe that's a regional BBQ thing. In most of North Carolina, particularly central and eastern NC, we are known for vinegar sauce. But equally important is that whole hog is the traditional meat source for this region. Once it's cooked, all of the meat from the whole pig is chopped up and mixed together. Shoulders, ribs, hams, loins, everything. This is often the case in South Carolina as well.
The resulting product is distinctly different from a traditional pulled pork shoulder and I love it. I grew up with it.
So for me, if given the chance to cook a whole pig, I'm jumping all over it.