Thinking in terms of the Spa Day refresh:
In terms of build/buy assets, an old fashioned scout tent would be nice, as well as more rustic furnishings, especiallystuff that has since been added to the base game, such as a bunk bed variant of the rustic log bed, or a new ladder perhaps.
In terms of gameplay, I can't see them going too adventurous, but I could see more woodworking and handicrafts (the woodworking table hasn't had much added to it since base game).
As mentioned before, I'd like to see a Park Ranger career that uses the herbalism, athletic and hardiness skills? Maybe they can stay for free in granite falls as a bonus.
We have aspirations already covered, and there is already the squeamish trait, but another trait they could add is the technophobe trait, especially if they add more off the grid stuff (I still hold out hope for a typewriter to write novels without a computer).
Ability to order herbalism ingredients from the computer maybe?
Lot traits/challenges would be a nice add since they were introduced after OR, but can't think what they could add.