Hopefully never, at least not in their current state.
I've said it a few times on HN, but web notifications are almost entirely used for malicious purpose. Copy-pasting from a comment I made previously on the topic:
> Take a look at your grandma's Android phone and she probably has 12 Chrome notifications saying she won a free iPad because she went on a site that asked to send notifications, and users are so used to user-hostile UX's that force you to agree to everything to use the site, they just hit "allow" so they can get to the content. I'm not surprised Apple doesn't want that on the iPhone.
I've said it a few times on HN, but web notifications are almost entirely used for malicious purpose. Copy-pasting from a comment I made previously on the topic:
> Take a look at your grandma's Android phone and she probably has 12 Chrome notifications saying she won a free iPad because she went on a site that asked to send notifications, and users are so used to user-hostile UX's that force you to agree to everything to use the site, they just hit "allow" so they can get to the content. I'm not surprised Apple doesn't want that on the iPhone.