Hello mate, glad you enjoy!
Every girl up to Sumeru will be added to the hot springs with a short scene/event. Beyond that, no girls will get the same treatment until after the game is complete and I make extra content as 'DLC', if I choose to do that at all.
I may add some small scenes/events/polaroids of newer girls at my own discretion and you'll get a nice taste of some of the newer genshin girls in v1.12.
-Mochi