Personally, I was hoping the Sims team would revisit either RoM or Jungle Adventure. RoM is pretty, but I find the endless grinding of spellcasting to level up to be boring, and the skill tree doesn't make each spellcaster as unique as the vampire skill tree does. Jungle Adventure has almost nothing to do in it. It's a new world that's pretty, but there aren't any puzzles to solve or missions to undertake in its leafy depths. It's a far cry from Sims 3 - World Adventures.
I like Spa Day as is. That said, I know there was a survey awhile back about community-voted stuff packs, and one of the options was about fitness and nutrition. Maybe some of that would make its way into a revamped Spa Day gp? That might be cool.