I really hope they will do all GP and that this first one is just a start.
For now our roadmap continues to be focused on improving content that’s in the game. That said, stay tuned – prepare your Sims for a relaxing refresh of one of our existing Game Packs coming up soon..
Because of the wording, I think either outdoor retreat or spa day seem the most likely candidates, and they are the most dated as well because these were the first two. Outdoor retreat really lost a lot of it's glance with rental homes becoming base game and tents being added in snowy escape and even batuu. Spa day is a decent pack but often overlooked because without a world, or aspirations it is a more subtle pack. You need to place a spa from the library before you can use the features. So it could do with a little freshen up as well.
I am curious to see how far they will go with the updates. Will we get new gameplay mechanics? Just new traits, aspirations, careers,... which are relatively easy to add because they are variations of existing features. Or just new objects and cas?
The GP I would like to see updated most is RoM. New spells, magic for children, lot traits to allow npc spellcasters to behave like they do in the magic realm, a magical leyline lot trait, better familiars, smaller cauldrons,... Even some missing furniture in the art nouveau set like a toddler bed or upper kitchen cabinets would be nice. So many possibilities. But I think they would have worded this announcement differently if it were RoM.