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.
If they did add Class Story Packs I'd prefer them to not costs CCs. After all, RotHC didn't cost CCs, it cost real money. Seems more palatable that way.