Very well put. I'd also add:
Ghosts (Base Game):
- Ghosts still run like they use legs so floating runstyle would be great for them.
- Better needs fulfilment for BG ghosts (more details here: https://forums.ea.com/discussions/the-sims-4-feedback-en/more-ghostly-gameplay/12254549)
Mermaids (Island Living):
- Turn the hydration need in a special bar like vampire energy bar (since they work similarly);
- Add "Underwater travel"interaction (similar to Tunneler werewolves): They should be able to travel quickly on water bodies knowing underwater tunnels;
- Add "Underwater food hunting" interaction (similar to Hunter werewolves): Living on water should be totally self sufficient for them.
