As part of the work to create core notifications system (as part of the yearly KR5.2 to simplify feature development on the platform) work has been done to unify behavior of notifications and simplify its operation.
As part of that work, we've identified several hooks that can be deprecated. Specifically, UpdateUserMailerFormattedPageStatus has no callers, and can be deprecated.
This also relates to the work on
- T373055: Explore replacing Enotif with an extensible notification system
- T128351: Notifications should be in core
See more information on the project on MediaWiki.