You're not wrong to compare the topics of fat fetish art and fart fetish elements, they're actually more adjacent then most people would think; both related directly to the digestive processes, at least, and burps are seen as far "lighter" of a thing despite similarity. I don't plan on drawing any fart fetish stuff but that could change one day I suppose, it's not a particularly massive interest of mine(I'm more of an oral-fixatory kind of person when it comes to fetishes) but it doesn't directly offend me if it's out of the way, I suppose. I don't like the smell component though and that's often emphasized in fart fetish material, which I think is where a degree of the distaste for it comes from- like I said, other than that I find it inoffensive. If you want an answer to your pseudo-question, I suppose you could consider a piece of two or art on that topic to be a faint but distinct possibility in the distant-ish future.