Google is reportedly working on a new feature that will limit push notification subscription to 90 days.
This new feature, which was first spotted by TheWindowsClub, could possibly discourage websites from abusing push notifications.
Users would decide when they want the alerts to stop, preventing a website from bothering you indefinitely or misusing notifications to send ads even after you believed notifications had ended. The default is currently set at 90 days, but this could change as the feature develops.
The feature is not currently available in Chrome Canary, as it was spotted in a Chromium Gerrit commit. It is reportedly on track to reach Canary builds of Chrome starting with 86.
Since this feature is still being tested and developed, it will probably be quite some time before we see it in a beta release or a future update.
Regardless of when it comes out, it will definitely be a useful feature because it may discourage sites from spamming users.