I have two levels of categories in my forum. I would like to allow users to change their notification settings on the top-level category with an option to apply this setting to the sub-categories within the parent. This prevents them from needing to react to category changes by once again updating their sub-category settings.
I’m thinking something like a checkbox to enable the notification selection to apply to all sub-categories.
a main section may have dozens of sub-sections, it’s annoying to mute them all manually.
I think a modal would be better. That way when you change your tracking status, we say something like:
Would you like to apply this change to *all* underlying sub-categories?
You're currently Watching 2 sub-categories, and Tracking 1 sub-category.
This is what makes it a not-so trivial change though. A convenience feature like this one needs to communicate very clearly what it does, so that users don’t shoot themselves in the foot. No one wants to make a mistake in bulk 
If a clear UX path is laid out, we’d probably be open to a PR on this one.
Has anything happened in this area? My categories are still a bit in flux, and they might continue to shift. I would like someone to be able to set a notification for a main category, and have it apply to all sub-categories, even if new sub-categories get created later.
To me, conceptually, a topic that is in the “Main - Sub” category is also in the “Main” category. I expected that watching “Main” would notify me if someone created a topic in “Main - Sub”.
Same here. We have been slowly creating a lot of sub-categories over the last few months, but only just realised we need to notify everyone to go and manually set their subscriptions to these sub-categories.
For me, the most obvious solution is to replicate the subscribe setting for all users on a top-level category to each new sub-categories created. This might result in a bit of over-subscription, but that’s easy for any user to correct via links in the emails.
Otherwise, Discourse is pretty fantastic.