Similar to other Atlassian products (namely Confluence) you are often notified on live updates to a page you are currently viewing.

It would be very helpful if this was put in place for Pull Requests in Bitbucket (Cloud, Server and DC) so that if a user is actively reviewing a Pull Request, they would be notified if the PR was updated (e.g. approved, merged, comments and commits added).

Notifications would be similar to something like the pop-ups in the top right hand side of the page so that the user can see there's been updates during their review.