I love this idea! I have to edit the calendar every time I switch households and I play 16-household-rotational-save. It's taxing and having options to limit holidays to certain households would save time.
Also love the additional suggestions about crossplay. Holidays are such a big part of cultural representation and also reflect personal-locale-identity. I would love to see more Holiday event options, there are too few and it feels repeative.
Also it feels like the devs forgot about this Holiday feature-system when adding new packs/worlds/cultures, since nothing has changed in years... it just feels stale and forgotten about, which is why these ideas are great and breathe fresh air into a dead feature.