Let's be fair. BG has Ghosts. GTW has Aliens. IL has Mermaids. StrangerVille...just strange, with Possessed sims and an obnoxious Motherplant.
Some of them offer more occult gameplay than the skeletons in JA.
However, I would certainly like to see some of the ideas from Happy Haunts return in a Gamepack, including a Grim Reaper 'career'.
A stuff pack would not be big enough. I'd say it would be a Gamepack since it's quite niche, but at the same time it should offer enough gameplay to keep occult players happy.