Bioware tried this already, when they put the Datacubes in the Cartel Packs. The forums got p-oed about it, saying that Lore doesn't belong there. I'm pretty sure they'd get ever angrier if BW sold Class Story content in the CM.
It's quite different selling something as a direct purchase, than putting on a gambling pack. I would imagine this wouldn't be done in the "story packs" model, where you would have the chance to get the story line you wanted and if you got one you didnt need you would just dish it out on the gtn, but more like a mini expansion sort of feature.